I think these are good guidelines for code that you have developed and absorbed the costs of research and development. But if you are getting paid to write the code then I think common sense (and most contracts that you will have to sign to close the deal) says that the client owns the code, since they paid for the R&D.

I always agree to give ownership of code I develop specifically for clients to them, but I charge for maintenance. This works well, because the client does not feel like they paid for something they don't own, and because I wrote the code I am defacto the best choice for maintainer (I don't obfuscate on purpose to achieve this, as that would make it more difficult for me to maintain it).