Fair point, Sayv, but it's a slightly different scenario with this particular market.
After all, the majority of games we used to play were singleplayer with multiplayer components. There was precious little (if any) expansion on said content, and when there was, you paid for it. Thus, Diablo II today costs me £5, but originally would have been £30. The point is, I'm still just getting Diablo II, and it's the same game it was on release.
In this scenario, however, more of the same is being added (recent expansion, for instance), and the overall product is actually improved and enhanced... and yet still costs less. You're buying (ideally speaking) a vastly superior product for a price lower than the specially-priced Founder membership had access to.
It's doubtless a good marketing idea, and the only people it might offend would be the Founders who already paid lifetime, so they can't really lose out... but it removed any perks of long-term loyalty, which is a bit of a risk, goodwill-wise.
I'm not sore about it, it's just a conflict of morals vs. marketing.