Last I checked the NBA likes their players to be strong. The guy isn't carrying around 30 pounds of gut, it's pretty much all muscle.
People get so hung up on height it's hilarious. If a guy can play, he can play. Royce is listed at 6'8" and I know there are always the message board psychotics who feel they can accurately judge a persons height or weight by eye sight from 50 yards away who feel that he is shorter than that, but shockingly, I'm going to go with what ISU has him listed at.
Off the top of my head here are some PF's of comparable size who have done well for themselves in the NBA:
Charles Barkley 6'5"
Larry Johnson 6'6"
Dennis Rodman 6'6"*
Elton Brand 6'8"
Jason Maxiell 6'8"
Elton Brand 6'8"
Carlos Boozer 6'9"
Shawn Marion 6'7"
Chuck Hayes 6'6"*
Carl Landry 6'9"
Anthony Mason 6'7"
Dejaun Blair, 6'5"
Paul Millsap, 6'6"
Clarence Weatherspoon, 6'6"
Ben Wallace, 6'7"* (his height by his own admission)
Wes Unseld, 6'7"*
* - Played a good amount of center
Common factor between these guys and Royce (barring the outlier in Marion) is that they are/were all extremely strong. To say that he needs to drop 30 pounds or he isn't tall enough to play in the front court in the NBA is all just ridiculous.