I think it's mainly because the shooting in PES 2011 emphasises the importance of a mixture of player atrributes (body balance, accuracy etc.), player positioning (whether your player has the space/is not being challenged) and the time you have on the ball more than in any other PES. If you have the space and time and you're shooting with a decent player i.e. a decent forward or midfielder, 9/10 you'll hit it on target with power - but of course this is in an ideal situation.
PES 2011 can be VERY unforgiving if you rush it, try and hit it off-balance/or when you're under pressure from the defence. With the tighter defenses in PES 2011 it can be difficult to get that time and space, so most are only experiencing decent/consistent shooting with those better players who have the ability to find that time and space for a decent shot. Also, long range shooting is a lot harder, it was quite forgiving in PES 2009/2010, but now you're only really going to produce a decent shot outside the area with someone in the 80s/90s shot accuracy/power ala Stevie G.
It's all a balancing exercise. I couldn't shoot for shit with Newcastle at the start of my ML, but I'm getting used to players now and playing to their strengths - put it this way if Carrol gets even a sniff of the goal inside the area it's going in the net as he's strong, balanced and powerful, but anywhere outside the box and he'll sky it.