Dennis Rodman was also little tough guy (Charles Barkley too) with a great rebounding ability , so i think there is an issue with motivation because we don't lose anything with loses or wins. Maybe he keeps his hands down to avoid any ugly injury. Let's hope he will improve his hustle on all sides (defensive/offensive) .
Second option is that he and others just leave some rebound for Tyreke to get a rookie award ?
People again and again use those two examples (Rodman and Barkley) for every short power guy in basketball, and its always a bad idea. They were one of a kind freaks of nature. The rules didn't apply to them -- basketball is a tall person's game. Being short in basketball is a huge impediment that only the special talents can ever fully overcome. Comparing a guy like Landry to those guys is like comparing some 5'7" guy down at the park to Spud Webb and saying, see? Spud could win slam dunk titles, so should you!
That said, Landry's boardwork is just such a distinct problem that its not about "ooh, he should do it just like all time physical freaks" so much as "ooh, I wish he could do it as well as David West", who sucks on the glass himself but normally keeps it barely respectable.