Anything that requires body contact, ie rbounding, interior defense, the Blazers are going to struggle at.  Taking charges is great, but at some point you have to make it hard to get into the key in the first place.

As for comparing LMA's rebounding at 6-11 to Barkley's at 6-7, since when is height the key to rebounding?  Wes Unseld was one of the top rebounders in NBA history at 6-7.  So was Paul Silas at 6-8.  Paul Millsap--at 6-8--is the only player in NCAA history to lead the nation in rebounding three years straight.  What do all those players have in common?  They're "wide-bodies."  If you are able to carve out a large chunk of space in the lane, that negates the reach or leaping ability of the guys you're rebounding against.

Also, whereas Barkley did most of his offensive work in the post--putting him close to the hoop for rebounding purposes--LMA frequently operates at the high post.  This is NOT necessarily a bad thing, incidentally.  When you have a center (in this case Pryz or Frye) operating down low, putting your four near the top of the key stretches the defense, creating scoring opportunities for your center or for penetrating guards.  (Nate never played Zach and Magloire together because they clogged the lane.) Sure, your four won't get a lot of rebounds when he's stationed out high, but neither will the man guarding him.

At the defensive end, Barkley was all about rebounding, but he was NOT about helping out on defense (and he wasn't built to be effective if he tried).  By contrast, LMA helps out continually--especially on penetrating guards.  That puts him out of position to rebound.  This is not LMA's fault; rather it's on the Blazer guards.  And remember: Zach Randolph's failure to help in those situations was one of the things that killed the Blazers in recent years.

Finally, the Blazers have been playing a lot of zone defense lately (mainly to cover for the defensive shortcomings of the guards), and it's always difficult to rebound when playing zone.  This is one of the chief reasons teams generally only play zone sparingly.  It's a straight-forward trade-off: you give up defensive rebounds (and subsequent fast breaks) in hopes of stopping dunks and drive-and-dish opportunities.

So while LMA's rebounding certainly needs to improve, there are valid reasons why his rebounding stats shouldn't be expected to equal Barkley's--despite LMA's superior height.  If LMA ends up being a 22 point, 8 rebound, 2 block, 2 steal guy, that'll be perfect.  And you can pretty well pencil him in for those numbers next season; he's practically there now and he's still a skinny sophomore.  The combo of LMA and Oden is going to be a nightmare for the rest of the league.

Not that those two alone should have to carry the rebounding load for the team.  Have you watched Outlaw, Frye, et al block out?  They frequently don't even remember to attempt it.  Those guys must improve also.  Like LMA, they presumably will as they mature.  But the Blazers will ultimately need to acquire rebounding help in the form of a Millsap-type rebounder off the bench.  If you noticed, the Jazz beat the Blazers with gang rebounding.  It wasn't just Boozer in there doing the damage.  They had a whole squad full of guys crashing the boards--each and every one looking more like a linebacker than a basketball player.  Kind of like a certain "Round Mound of Rebound" (aka "Sir Charles").