Responsibility chart

Joseph has been a good helper since he was first introduced to the concept of helping mommy by putting small items of clothing in the dryer for her. He does help 'at will' though. And does not always obey mommy and daddy when they ask him to do something. At two and a half, it is time for some training.
This saturday we went to ToysRus where they had a birthday party for Thomas the tank engine. It was not as well organized or elaborate as I had hoped, but one of the main atractions was the chance to play with some of the engines on a train table. Joseph has discovered the joys of Thomas and has become rather enamoured with the idea of owning all eight engines that are mentioned in the Thomas song. Currently he is missing Gordon, Edward and Henry, and at the store he was allowed to play with Gordon and drive him all over the extensive tracks.
I appprove of Thomas since it's a simple, wooden train set which stimulates fantasy, the lessons from the books and episodes on tv are nice and the trains work with the generic brand tracks. Still, that does not mean that Joseph should get every train he wants just because he wants it, right?
Ever since last saturday though, Joseph keeps asking for Gordon, insisting we go in the car and go to the store for Gordon. I keep explaining to him that things in the store cost money and that daddy works very hard for that money and we should not want everything we see. But of course, that is a lot to understand.
So.. I decided to let Joseph earn Gordon with his very own chore chart. A quick google search gave me this website which has a responsibility chart for young children: http://www.freeprintablebehaviorcharts.com/daily%20routines.htm.
Joseph needs to help mommy dress him, go down nicely for nap and bedtime, pick up his toys and be nice to his brother (I changed that last one from the chart since he doesn't have much oportunity to share his toys yet).
So, after printing the chart I tried to explain Joseph the goal. The chart is on the fridge and each time he does something right, he can earn a sticker on which mommy draws a smiley face. At first he seemed more interested in the stickers than anything else. When he had been helping mommy to dress him and mommy drew the first sticker, Joseph asked for the sticker to be put on his arm. I obliged and drew another one for on the calendar. Then with much fanfare the first sticker was put on the calendar.
Half an hour later, while eating some blueberries, Joseph asked for Gordon again. I told him he would have to earn Gordon and explained the system once more of the chart. This time a light went on.... because the next thing Joseph did was taking the sticker off his arm, going to the chart and very precisely put that sticker next to the previously earned one...

Should I be proud of his inventivity? OR afraid he will grow up trying to cheat any system. Oh help... he might become a politician!