I'd like to remark that the linguistic arguments of Jehovah's witnesses are based on the fact that is not certain if Jesus died either on a (single) torture stake or a (tradinally shaped) cross. Rather they feel the language used in the NT is not sufficiently clear on this point. Therefore they stick with the basic meaning of the NT word (stauros) as a 'torture stake'. By translating it with a 'cross', they feel they risk adding something to the word which might not be intended by the original authors in the first century.
Recently, there has been a Ph.D. study published about this very subject. The author basically agrees with this linguistic argument of Jehovah's witnesses.
Gunnar Samuelsson, Crucifixion in Antiquity. An Inquiry into the Background of the New Testament Terminology of Crucifixion, 2010, 413 p. (published in 2011).
- A short outline of the book's content
The author investigates the philological aspects of how ancient Greek, Latin, Hebrew, and Aramaic texts, including the New Testament, depict the practice of punishment by crucifixion. A survey of the ancient text material shows that there has been a too narrow a view of the “crucifixion” terminology. The various terms are not simply used in the sense of “crucify” and “cross,” if by “crucifixion” one means the punishment that Jesus was subjected to according to the main Christian traditions. The terminology is used much more diversely. Almost none of it can be elucidated beyond verbs referring vaguely to some form(s) of suspension, and nouns referring to tools used in such suspension. As a result, most of the crucifixion accounts that scholars cite in the ancient literature have to be rejected, leaving only a few.
The New Testament is not spared from this terminological ambiguity. The accounts of the death of Jesus are strikingly sparse. Their chief contribution is usage of the unclear terminology in question. Over-interpretation, and probably even pure imagination, have afflicted nearly every dictionary that deals with the terms related to crucifixion as well as scholarly depictions of what happened on Calvary. The immense knowledge of the punishment of crucifixion in general, and the execution of Jesus in particular, cannot be supported by the studied texts.”
Since the author was frequently quoted in the media as a person who doubted the crucifiction of Jesus, the author, who is not a Jehovah's witness but a protestant pastor, has his own website in which he tries to take away some misconceptions.
See also for general information: Wikipedia.