As someone who prizes his high quality movie torrents, I can testify that files over 5GB in size don't stay adequately seeded for very long after their initial release.
It seems like an arbitrary limit, but an adequate one for the time being.
I wouldn't think it's hugely limiting. In practice I'd speculate that the majority of torrents out there are either around 180MB, 370MB, or 1800MB
If (for whatever reason) you choose to use S3 as your tracker, then you just need to commit to breaking your >5GB content lumps up into multiple pieces.
You're probably right that the majority of torrents on the internet line up with the common TV show sizes, but it doesn't at all follow that users of this service will follow that distribution.
I have 60gb files in S3, and saturating available bandwidth to download them in a reasonable time frame if they're not in the same country is actually a bit of a challenge.
Bit torrent would be one of the fastest and fault tolerant ways to retrieve the files, so it not being available stings a bit.
While I'm trying to download large files on consumer internet, I'd imagine that huge files between geographic locations and server grade connections would face a similar problem.
