Two thoughts:
Firstly I think I remember rumours or confirmation when Dungeon and Dragon were first licensed out to Paizo (which, I think, was created precisely so that Wizards had a company to license the magazines to!) part of the reason was that Hasbro sees itself as a games company, and doesn't
do magazines. They didn't understand them, didn't do them in any other division and didn't really want to be doing them in the roleplaying division, or whatever Wizards is considered. So it might well be that Wizards is not permitted to publish print magazines like Dungeon and Dragon. Given that Paizo continuing to do so would be in competition with some of the content of the DI, it makes sense to end the print magazines for good.
Secondly, what I found most interesting was the comment of Matthew Sernett in the 'Reflections' article:
True, paper issues won’t litter the floors of future game designers, but their contents, after having been on the periphery for so long, will once again be brought into the fold and become an integral part of the future of the D&D game.
I
think what he's saying here is that for a whole host of reasons, Dragon material isn't really considered to be D&D material. If Wizards writes up a feat or spell or class in a book, people consider it to be D&D material. They might decide to use it, or not use it, but it's considered 'official'. Despite '100% official material', I don't think the same is true for the material in Dragon. It is certainly not used by Wizards as 'official' material - it doesn't show up and inform later products the way that spells from SpC or feats from Complete Arcane do. By bringing this kind of content back in house, it suggests a far closer link between D&D R&D and the material used - and quite possibly a two-way relationship between the material you get as part of this subscription and the future direction of the D&D game.
Perhaps ...! I ought to say, I'm pretty neutral on the issue, having only occasionally bought Dragon, and never Dungeon. I agree that Paizo have done the PR superbly well, however - well enough to convince me to subscribe to Pathfinder!