We have three Roku's and all of them appear to be uploading relatively large amounts of data.
Appoximately (in Megabytes):
1. Download 21,786 Upload 271
2. Download 209 Upload 27
3. Download 7,970 Upload 45
This information was provided by my AT&T Gateway, BGW210-700. I reset the data so this is showing a few days worth of data.
While 271MB might seem like a lot, compared to 21GB it's about 1%. That's normal. Packets have to be acknowledged. Data is going in both directions just to maintain the connection.