With all the talk about how goyim dress/dressed, it should be pointed out that pashtus, there’s an inherent aspect of covering the head – modesty and subjugation to the King – which doesn’t change with the times. The changing styles indicate that society has regressed in these areas, but we shouldn’t.
So while one may argue that it’s no longer an absolute chiyuv to wear a hat to daven (which is harder to argue for a jacket), it’s pretty clearly at the very least a maalah.
See ‘?”? ?”? ?:
http://hebrewbooks.org/pdfpager.aspx?req=14170&st=&pgnum=147