Yeah, I reeeaally doubt WotC's going to be knowingly doing anything that would even indirectly lead to people being encouraged to not buy the core books. Even if it seems that way from early rumors of the database.
I agree that in the long run, minimal investment would amount to just the core books as they get released yearly. KotS isn't even needed at all, if you bought that it's because you wanted it, not because it was a required part of the buy-in, which as far as I can see is 3 core books ($60-90) a year. DDI by itself would come to 15*12=$180 a year if I'm not mistaken.
I agree that in the long run, minimal investment would amount to just the core books as they get released yearly. KotS isn't even needed at all, if you bought that it's because you wanted it, not because it was a required part of the buy-in, which as far as I can see is 3 core books ($60-90) a year. DDI by itself would come to 15*12=$180 a year if I'm not mistaken.