Are there even any Roku games that you can play holding the remote sideways and using the A and B buttons? I have a Roku 2 XS (bluetooth remote), and I'd tried a lot of the free games and haven't found one yet. I'm thinking I'll offer it as a menu option for my game, so people with a remote with A and B buttons can finally use it sideways!
See viewtopic.php?f=34&t=67758&p=432541#p432492 for the experiments i did and then can try out with a WiFi Direct remote.
The limitation seems to be remote-related, so it won't matter if one uses SDK, NDK, MDK, UDK et ceter-ay.
I don't know for certain, but I feel fairly confident saying that it's not the remote. It's much more likely that they just haven't exposed multiple keypresses to the BrightScript layer (yet?).
Based on recent experience, my view is "evolving" from "it's a remote limitation" (above) to what TheEndless said (below).
event = wait(1, port)
if (type(event) = "roUniversalControlEvent") then print event.GetInt()