It's also worth pointing out that sales and development have substantially different work cycles. A sales is a binary event, once it's done, it's done. Development on the other hand is (mostly) never complete. There's maintainence to do, features to tweak, bugs to fix and so on.
Let's consider a bug report. Let's assume the client is not paying to get the bug fixed. Which developer then wants the job? Indeed since programmers are incentivized the same way as Sales, they need to "complete" lots of jobs quickly. The faster the better. Which leads to more corners being cut in the first place. Worse code, no-one interested in maintainence - these are not recipes for quality products.
One of the bigger problems with commission based salesman is they they'll sell anything - limiting them to selling only what is already available takes strong management, and the occasional waving of a big stick. Our sales people work inside some tight constraints and are financially penalized when they oversell. This is a reaction to past sales people overselling, angering their commission, but for work which was ultimately unprofitable because they mis-sold the client the wrong product.
Culturally sales people are used to a commission -programmers are not. Sales people sell a lot of things that are eh to sell, and avoid products that are worthwhile, but hard to sell. If programmers were the same way we'd end up with mountains of 99c apps that do nothing as programmed searched for the killer app that takes no risks, but is easy to sell. Oh wait...
A single developer is ultimatlely paid on commission already - but he's also motivated by the health of the business as a whole. The employee working on commission enjoys none of the long-term upside of the business, yet shares in all the short term downside. He'll naturally want to work only on the "hits" and will quickly abandon projects if they're not an inmmediate success.
We could also talk about co-operation (sales is notoriously insular, whereas programmers benefit from being sharing knowledge), the whole concept of "after sales service", and so on, but I think you've got the point.
It's good to ask this sort of question- but in this case I don't see any benefit in paying them on commission, and I predict it would optimize developers in all the wrong sorts of ways, ultimately resulting in very bad code.