I checked with FMCA Tech Connect and below is their response:
This is a true statement. As part of the plan details it states that video streaming will typically stream at DVD quality (480p).
As you know, we tested the Wi-Fi during October using the 50-inch TV that we’ve brought down to conventions. We were able to stream 1080p with no issues.
Josh went down to our Roundbottom office yesterday to get the TV and brought it back up to Clough. We tested again, same results. No buffering or lagging while streaming on 1080p.
The T-Mobile plan states that Video typically streams on smartphone/tablet at DVD quality (480)p
Hope this helps.