No,I don't think there is a migration going on. This site has a decent number of postings late afternoon weekdays,but is often quiet later. The sheer volume of questions asked on the other site all day,every day (including weekends)is far greater.
We can't claim a better quality of poster either. There is still an amazing number of people who can't be bothered to give clues or number of letters. Wrong clues,wrong number of letters are also common. About half of posters never say thankyou.
We also get, what for want of a better word, I'll call malicious posters. The sort who are too gutless to say something possibly controversal in their usual name so use an alias. Like my idiot namesake who regularly revives the "posting hints for this forum" thread.