The lack of lots of dragon powers has been a reaction to the "dragons are too complicated" movements of the past 8 years. The argument goes that dragons in 3e had so many powers that they never even got to use them all against PCs. This was true in my experience - I mean, sure, they had lots of room for utility powers, buffs, etc. But how much of that was spelled out in the MM?
At one point last year I took note of all the "big ticket" monsters and their special powers, while I was preparing a shapechanging character. I took note of how many of them had special powers that WEREN'T in the stat block; are you aware that monsters like Pit Fiends, Solars, etc. have anywhere from TWO TO FIVE powers that SHOULD be on at all times, but AREN'T in the stat block? The pit fiend should probably be at least four points higher thanks to unholy aura, but it isn't in the block. The solar has a +4 in the spells list that isn't in the stat block, and as a 20th level cleric has at least a dozen multi-hour spells that would affect his armor, saves, and to hits, but don't because they're wary of things like dispel magic, etc. affecting the totals.
Same thing with dragons; even something like a Mage armor spell (or greater mage armor, if you're a spell compendium kind of guy or gal) would add +4 to +6 to AC, and it's not accounted for, unless you're just that into bookkeeping. They've simplified some of this for DMs by assuming such effects are already in there, and they've also as a side product reduced the number of ways you can dispel magic, if the dispel magic example is any judge. So the truth of the matter is, if you want a more versatile dragon dragon, there are ways to do it; however, it's been my experience that that multi-faceted dragon with all the different class levels, and spells, and special qualities wind up dying within two or 4 rounds of meeting the PCs, and the 8 1/2 x 11 or A4 page of stats you just typed up wind up getting tossed, or recycled on the next time you run a dragon of similar age and type. If it's been a DM advice for years not to overprepare your NPCs more than you need, then the same wisdom should apply to monsters, as well.