Paul Thurrott mentions that the reason the iTMS isn’t selling full-length movies could be:

To put out an equally ridiculous question: Is the real reason iTunes isn't selling full length movies yet because the iPod only gets 90 minutes--if that--of battery life when playing back video? Methinks that's a much bigger issue for Apple that the price.

Is this the case? Not for me, I’ve gotten at least 4 BSG episodes on a fully charged battery out of my 60GB Video iPod. If you figure that each episode is on average 43 minutes in length then that means I’m getting approximately 172 minutes of battery on a full charge. That’s just shy of 3 hours which won’t allow me to watch all 10 episodes of Band of Brothers, but more than enough for me to get to see an average full length feature film.

Paul also (apparently) hasn’t heard of the iLuv i604, a relatively inexpensive ($84.95), external battery pack (with nice integration) that extends the battery life of a 60GB Video iPod up to 55 hours. iLuv also provides the i603 for the 30GB Video iPod that provides for a 42 hour battery life.

Either solution would allow me to watch all of the Battlestar Galactica to date (Miniseries = 3.4 hours, Season 1 = 9.4 hours, Season 2 = 14.9 hours) which totals 27 hours and 53 minutes as well as fitting in a few full length feature films in there.

I would say that the more logical reason for not having full length feature films in the iTMS has more to do with distribution channels/partners and Hollywood’s inability to understand the market place than anything else.