Part of the problem is that Ancestry is trying too hard to be all-knowing. They refuse to share their information with us, so we have to guess. They don't even provide a list of the different ancestral groups they're using to classify people into, let alone what they think they all mean (because God knows they don't mean what ANY other genealogy company means with the same terms). Getting the raw data files they've promised for 2013 will help, but they need to be more transparent period. The other companies are. We shouldn't have to speculate about whether or not they use phasing or where; it should be in an easy to find FAQ.
I guess it makes sense that people with long histories in the US would get the best matches, since that is Ancestry's specialty, databases of American records. I'm hoping the rumors I've heard of FTDNA being the best place to match with other Jews will turn out to be true; my transfer there (from my 23andme test) should go through in a couple of weeks, or so they tell me.