I have in mind this particular developer, he is no longer visiting this forum, other members complain for him not responding emails. So business cannot relay on individual freelancer..
PS his addon work, licensing relay on his server, here is a good example of what may happen without any prior notice
http://www.mysticthemes.com/
Just like to explain how tax system work here in europe. amount + tax, if business is tax exempt with valid vat, them amount without tax. But if for any reason addon would say business vat nr is OK wich is not, then tax man would tell me to pay tax out of my pocket. So risk of the loss is huge, it is not some design or speed element..
Why not rely on 3rd parties. It keeps the core cost down and usually provide better service/responsiveness. You can get a 3rd party developer to do an addon if there is a market for the addon functionality. Addon products are cheap in the grand scheme of things. Custom development (or core development) is not. For business critical functionality, spending $50-100 (or other small amount) means nothing if it saves you time, reduces administrative cost and improves your accuracy.