All aspects of a game are given a priority. Once that aspect has made enough progress, the team may be moved to develop another part of the game. So dragons were developed to a point where they would fit into the game. Then they went off to work the game to shippable status. If they had time a team would go back and refine that experience. Bethesda as a developer, probably will not change this aspect of the game in a patch because Publishers are not going to spend money to have a team work on it.
I just gotta say, Patch 1.5 pretty much disproves your point here. Bethesda went back (For better or worse) and worked on Killcams (Including new Animations) and better underwater transitions. While completely overhauling Dragon AI would be highly unlikely, as long as the community continues to support Skyrim, they can change and add whatever they want, Assuming there's not some huge programming-related issue, even giving Dragons different shouts, or even a little AR would solve the issue. Just for example of the "Shouts" each dragon can be given:
But they feel like they're too much of a focus of the whole game, not just the Main Quest, and if seems like you get them a little too fast. A bit more Buildup would have been nice, even so far as to be unable to shout until you recover the Horn of Jurgen Windcaller. That way, players who don't want to be "Dragonborn" can still enjoy killing dragons.
Speaking of which, probably my biggest issue with the Dragon Shouts, is that the dragons don't even use them... They really pissed away a great opportunity to make Dragons true boss fights, instead, the Draugr are more dangerous, because they can shout you to the floor and pump you with a quiver of Ebony arrows. I mean, really!
Lesser Dragon(Fire) - Fire Breath, Unrelenting Force 2
Lesser Dragon(Ice)- Frost Breath, Unrelenting Force 2
Blood Dragon(Fire)- Fire Breath, Unrelenting Force 2, Dismay 3
Blood Dragon(Ice)- Frost Breath, Unrelenting Force 2, Dismay 3
Frost Dragon- Frost Breath, Ice Form 1.
Elder Dragon(Fire)-Fire Breath, Unrelenting Force 3, Marked For Death 1
Elder Dragon(Ice)- Frost Breath, Ice Form 1, Marked For Death 1
Ancient Dragon(Fire)-Fire Breath, Unrelenting Force 3, Marked For Death 3, Storm Call 1
Ancient Dragon(Ice)-Frost Breath, Ice Form 3, Dismay 3, Storm Call 1
Alduin- Unrelenting Force 3, Meteor Storm, Become Ethereal.
But nooo, Dragons can't use Dragon shouts!

