In said:
Nonetheless, the phrase "thanks in advance" presumes an unwarranted
obligation on the part of the person to whom it is addressed.
1. On Usenet, posts are not addressed to any particular person. It's
an abbreviation for "thanks in advance to whomever might reply to my
question" and there is no unwarranted obligation towards anyone
presumed.
2. In real life interactions, it is not uncommon for polite persons to
say "thank you" (honestly, not sarcastically) even when the other
person could not provide any help. This debunks your interpretation
even for the cases when TIA is used in private email.
It is used in Usenet postings by people to avoid responding to help they
may receive.
I find followups along the lines of "thank you to all those who
answered my question" a lot more obnoxious.
Personally, I prefer the simpler "thanks" formula. It can be interpreted
as "thanks for reading my post" by those who don't intend to reply and
as "thanks for answering my post" by those who post helpful replies
Dan