Li-Po battery technologies work a little bit differently than previous battery technologies (Well, current battery technologies in the PC world, they still haven't quite decided to move into the 21st century with batteries).
LiPo batteries will have a gradual, yet fairly quick drop off down to around 80-85% capacity. Then they will hold this capacity for a great amount of time (this is what makes them so good, they hold most of their capacity for a really long time). THEN, they will start to drop off very rapidly towards the end of their life and fail completely. This 'stair step' way of losing capacity is sometimes confusing when you are used to the gradual loss of capacity over time like with a Li-Ion battery, but it is normal.
For the record, even though a LiPo will drop off very rapidly at the end of it's life, that point at which it begins to drop below 80% is generally hundreds of cycles after a Li-Ion battery has failed completely. Some people have said that LiPo's either work, or they don't. There is no middle ground, and that's mostly true!
If it were me, I wouldn't worry about it. That SMC utility is not the tell-all end-all, it can be inaccurate. It's likely going to hover around 80% for a long time. The real tell is how long your battery actually lasts in your daily use. I suspect it's still close to where it was when new, and I suspect it will remain close to where it's at now for another several hundred or even 1,000 cycles.