I don't read many contemporaries.  When Beth challenged me to do a SBD's article on why I prefer historicals, I had to stop and think (oh, the pain).

I think the main thing is suspension of belief.  I have a difficult time suspending belief with a contemporary because so many things can just jump out at me.  For example, years ago I was reading a category romance, the heroine was an astrologer.  Several times it was mentioned that she was a Capricorn.  Then there was a big scene where they had a picnic to celebrate her birthday.  I'm a Capricorn, we don't get many picnics between Dec 22-Jan 21 or so (no she wasn't in Australia or the like, it was somewhere like Kansas).  Couldn't finish the book.

Now with a historical, it is easier to distance one's self.  While I have been called a Regency Freak because I somewhat understand the ins and outs of peerage (or at least where to find the references), there's so much that just isn't within your day to day reference.  For example, Nicholas and Bella leave a ball, if I get (God forbid) the type of carriage wrong, it isn't the same as if Ethan and Hope drive off in Ethan's Edsel.  In the latter, you have immediate reference (except for my carriage experts).

The other thing is I can accept that a historical heroine is not a feminist icon.  For the most part, her job is marrying well and producing the heir and the spare. (There is a lot of leeway in that, however).  But it's so much more difficult for me to accept contemporary heroines (non romantic suspense) because they tend to be more traditonal. 

So in a brief nutshell, that's my reasons and I'm sticking to it.