Like you said, it's about competition.
I have often found that for exact match domains in uncompetitive industries can jump onto the first page within a week or two without much more than an index page and link or two pointing to them.
These days, lack of competition plays a big part in which domains I choose to develop first. It's much easier to get traffic (and cashflow) with low competition niches, even if it's not the big dollars, which is much better than outlaying quite a bit in order to rank well in more competitive industries even with exact match domains. Often it can take many months to get any traction in more competitive industries. So that means it takes months to see any ROI.
I'm actually starting to think that the domains that I bought in the highly competitive industries (credit, law, insurance, accounts, etc) despite reasonable search volumes, might not even be worth the effort of developing at this point.
