Apart from the fact that it's really only the dedicated fans who even know of their existence. The last two might be headed for rerelease this year but only in a frustratingly limited format, although that in itself begs the question of how greedy he really is. Surely if he wanted more money they would be released just as standard CDs.
I think the main proof of the argument lies in the fact of the selectivity of these reissues, like the 30th anniversary range, with their "rare" bonus tracks which, in the case of Ziggy, was manufactured specifcially for the release, and in most other cases are simply edits which anyone with the right software could make on their own. However, there is the counterclaim that he could just have easily released truly rare material on them to encourage more fans to buy them.
Perhaps that's the issue, how he treats his fans with regard to what they'd like to see released. Obviously he wants to make money from his music (what musician doesn't) but how interested is he in keeping the hardcore fans happy when he knows they'll pretty much buy anything anyway?