It originally read (abbreviations expanded):
Welcome to question(s) and answer(s) site for [site-specific description]
That is grammatically incorrect. It was changed to:
Welcome to questions and answers for [site-specific description]
I don't see the problem here. This is correct.
Stack Overflow houses questions and answers for professional and enthusiast programmers, so when people get here we say "Welcome to questions and answers for professional and enthusiast programmers".
Instead of saying:
"Welcome to questions for professional and enthusiast programmers and also welcome to answers for professional and enthusiast programmers"
we just say
Welcome to questions and answers for professional and enthusiast programmers"
Another way to put it is that you are welcome to the questions and answers housed on the site, hence we welcome you to questions and answers.
For what it's worth, I asked in the EL&U chat and on the main site. The one person who responded in chat said "what is written is fine as it is". The jury is still out on the question on the main site, but at the time of this writing, the votes seem to be leaning towards leaving it as is.
<sitename>
, which is described as "Q&A for<whatever>
".