It isn't horrible or indefensible -- it is just a bad idea. Six months is a long time. There is plenty of 3.x gaming left to be had. What's more, making people think of e-Dragon as the first, best place to get their D&D fix is good for the future of the magazine and therefore the D&DI and therefore D&D. Simply ignoring a segment of the player/consumer base -- the people that like to use new crunch, even if they homebrew their own setting and adventures -- in hopes that they'll stick around anyway strikes me as both dubious reasoning and more than a little insulting to that player/customer base.
But then, it seems that WotC's attitude has been, since the announcement of 4E, that D&D players and DMs will go along with whatever, simply following the brand without question. I hope they are wrong. I hope everyone who is dissatisfied with the electronic Dragon refuses to subscribe to the D&DI; I hope that everyone who doesn't like the 4E design philosophy simply doesn't buy the new edition; I hope that those that prefer D&D as it is support those companies that continue to produce quality 3.x materials. Whether or not these people are enough to make a dent in WotC's bottom line is irrelevent -- the point is that no company, especially one that produces entertainment, should feel so confident in their brand power that they are willing to wager a portion of their paying customer base without suffering the consequences for doing so.