That's pretty much par for the course with laptop batteries. The two worst things you can do to a Lion:
A)Keep it fully charged and hot. B) Cycle it from fully charged to dead flat.
Both are things that most people do. When you run your laptop plugged in, the charger charges it fully, and the running laptop gets quite hot. This is hard on a Lion. The other thing people do, is run mobile until the battery is dead and they shut down. Then they charge it when they can. This also is hard on a Lion.
The best thing to keep your Lion alive is that when you're plugged in to power, charge it half way, then remove it from the computer so it doesn't get hot. Only fully charge it when you need to go mobile, and shot down when you're maybe around 25%. Now, who does that?