Yes there is a difference, it is much better to have 10 backlinks from 10 different sites. Better still to have 10 backlinks from high-PR sites or from .EDU or .ORG sites
It's best to have your own domain name and web hosting, so you are totally free and not afraid to see your blogspot blocked for some reason. Choose your webhosting company wisely as it can be very annoying to move sites around once you've established them somewhere and you realize your webhosting company sucks.
There is a thread about micro site for adsense at http://forums.digitalpoint.com/showthread.php?t=2515546#post17841129 hope it helps.
I think you hit on all of the key points that are in most of the books on making money with adsense. My opinion is that with adsense you either need to have a blog or website that ranks on page one of Google searches or have 50 sites that are getting a few hits a day. Either can work, but PPC is tough. Maybe it used to be easier, but there are a lot of sites now. A lot of competition. ~Lynn .