That's what we like to hear - glad that it's stimulating your mind
The reason we chose a simgle API for all entries is that of a level playing field - as you can see from the announcement positing, there are a number of judges involved in selecting the final five, and we felt that placing this limit on entries allows us all to have a baseline - a frame of reference - to assess your entries on. For your entry to be valid, it must work with the template API, although once this is all over and the winners announced, by all means: go nuts! You might even find someone else's submission better than yours, which will give you an even better platform to create a new version from.
Although using the event structure and mouse input VIs are native to versions above 6.1, there may be methods that you can use to complete the tasks with 6.1 (I'm not saying there are, nor am I saying there aren't ). There are still plenty of people out there that are still using 6.1 (it is a pretty stable and functional version), and we didn't want to exclude those folks from entering the challenge.