I don't know why people are still acting like cutting out the GBA functionality of the DSi is that big of a deal. Or at least, like it was that big of a surprise.
I mean, have people forgotten when the latter GBA generations took away GB/GBC functionality? Or hell, taking it back even further, remember when GBC came out, and eventually, "GBC-only" games were released for that system, "forcing people to upgrade"? How is that any different from what's going on now, really?
In both cases it was something to be expected. Companies do these types of things to either a) do more to streamline the portable, as a whole and/or b) to make money by forcing people to upgrade if they want to "stay in the game". Truly, the old saying of how "there's nothing new under the sun" stills holds true, because it's the same [parasitic bomb], just different day and age.
What happened with the DSi, is basically, more of the same. And likewise with the various Sony upgrades over the years. They only did more to copy the example that Nintendo and Sega did years ago, after all!