I can name another AIC show that changed styles 
from OVA to TV. . . Vampire Miyu! I doubt I'll 
get any arguments. ^_^  In the case of Miyu, I 
think the change was definitely to save time. 
When you're doing only a four part OVA, you can 
take the time to do that kind of animation. But 
just try to keep that up for a twenty-six episode 
TV series! (*shiver*) They'd be working on it for 
the next forty years. ^_^;

Many Sharp Smiles,
--Drac