I would just like to point out another difference between these verses: according to the NIV translation, Matthew's Gospel includes "wife" as someone you could leave and then be rewarded for leaving. But in Mark's Gospel, (in the NIV), "wife" is not included.
But the KJV of Mark 10:29 does include "wife," and to that I say: a false translation. Nearly all other Bible translations (NIV, MSG, Einheitsübersetzung, +more) do not include "wife" as someone you could leave and then be rewarded for leaving. And why would Jesus say that, when just 18 verses earlier, Jesus was stressing how wrong it is to put away your wife... Regarding the "original text" - many Protestant Bibles (like KJV, Tyndale, Luther) include the word "wife" because of Erasmus' (the 16th century Dutch Priest who kindled the Reformation) first "comprehensive" Greek Bible (1516) that also included the word "wife" (or in Greek: Γυναίκα, in Latin: uxore). It served as a critical edition of Jerome's Vulgate in 384 AD and a synthesis of various Greek manuscripts available to him at the time (reaching as far back as the 4th century). ATTN: Jerome's Vulgate (the Latin Bible that the Catholic Church ascribes to) doesn't include the word "wife"! As grateful as the world can be for the sincere Christian efforts of Erasmus, his Greek Bible (since known as Textus Receptus, Latin for "received text") resulted in the Bibles of the early Protestant branches of Christianity to falsely include the word "wife" in their translations of Mark 10:29.
Since that time though, other and even older Greek manuscripts have been discovered. And many do not include the word "wife" in Mark 10:29. Now, of course the 1st edition manuscript of Mark's Gospel is lost. The oldest, complete Gospel-text manuscript is Codex Sinaiticus, a Greek translation from approximately 325 AD - it does not include the word "wife." But perhaps the oldest relevant manuscript is a text by Clement of Alexandria, a Christian-convert Theologian from Greece (c. 150 - 215 AD). He published "Quis dives salvetur" ("Which Kingdom Will Be Saved") in 200 AD and therein quoted Mark's record of Jesus speaking to the rich young man. When he quotes Mark 10:29, Clement does not include the word "wife." With Clement being only 2 generations away from Jesus Himself, his quotation appears to be the most definitive and reliable source of Mark 10's original text.
So, no - there isn't really a "leave your wife for the Gospel" teaching in this verse. One could say "well it appears that way in Matthew and Luke." Two things: First, Mark's Gospel was the first collected Gospel-narrative that was circulated among the early Saints. When the text came to the Matthean Saints, these were of course the more "Jewish" Saints that come from a tradition where a man actually could "leave his wife for God." So when the Matthean record was made approximately 10 years later, the text presents a conflict that the Markan doesn't... In Mark, there is a parallel if-then clause: IF you leave house, parents, land for the Gospel's sake, THEN you will receive hundredfold in houses, parents, and lands (no mention of "wife", because in Jesus' Christianity, we don't have any tenets of numerous - "hundredfold" - wives-reward in an afterlife). In Matthew, a conflict arises in the if-then clause, because, apparently, IF you leave house, parents, land, or wife, THEN you will receive a hundredfold... Wait, a hundredfold of wives??? That may align with Judaic or Muslim tenets, but not Christian. The same conflict arises in the Lukan record: IF you leave house, parents, wife, THEN you will receive "manifold more in this present time."
One might perhaps argue that the expression of receiving manifold "wives" through Christian conversion is simply a way of saying that you enter a big Christian family where everyone is related through Christ. No. Think of Paul: he was very clear in the expression of all female Saints in the Family of Christ as being "Sisters" to the male Saints. Not wives.
So in the search for the original words spoken by Jesus of Galilee, and in striving to resolve the discrepancy between the Gospel records in light of ancient manuscript discoveries, truth points to Jesus teaching that a Christian man will be blessed for leaving behind his land, his work, his friends if it is to magnify Christ's Kingdom. It is also appropriate for a man to leave behind parents (as Moses taught in Genesis, and Jesus quoted 22 verses earlier) to cleave unto his wife. A time will come in a Christian man's life that he will even have to let go of his children, let them grow up and follow their father's own pattern of Christian living. But a Christian man will always have devotion to his wife, in unity with his devotion to Christ. In fact, Paul taught that a husband's loyalty to his wife should reflect Christ's loyalty to His people, the Saints (Ephesians 5:25). Peter lived this teaching to the end. He not only took his wife with him on his Christian missions (1 Corinthians 9:5)... According to Clement of Alexandria, Peter led his Christian ministry so close with his wife, that they were both martyred and crucified on the same day. Living in Christ, dying in Christ, a Christian marriage goes on in the hope to live eternally in Christ. (Revelation 19:6-9)
Comparison of Greek manuscripts, oldest dating to 4th century
Quotation of Clement's quoting Mark 10:29 in "Quis dives salvetur"
Overview of "Quis dives salvetur"
Comparison of KJV w/ other translations of Mark 10:29
Westcott and Hort's odd commentary
Mark 10:29 in Codex Sinaiticus
St Jerome's Vulgate, Mark 10:29
For a future discussion point: