I've been using PICAXE commercially for years now, basically ever since Stan Swan made us all aware of them in Silicon Chip a few years ago.
Having also played with the Parallax BASIC stamp(1 and 2), which is a similar concept, but about 10 times the price per unit, so PICAXE was a natural path to take. That, and PICAXE are available in both standard DIL and SMD packages, which is extremely useful for small projects - the BASIC Stamp cannot compete here in terms of size.
On the code front, source-code is closed for exactly the reasons that Marcwolf mentioned.
If the customer wants things to happen differently, I can write changes to the code during roll-out, and am happy to re-program any units for different operation as part of the service-contract, but I would NEVER release source code, as someone with an ego and a little knowledge is a very dangerous thing, if you let them have the source code!!!
I do have an escrow agreement with all my clients, in that if I was to be hit by a bus or otherwise get a terminal medical condition, all details including the code, schematics, PCB layouts etc, are released to them via the company lawyers, so that they can continue to use the product, and find someone else to administer to the system if I am no longer here.
An escrow is quite easy and relativey cheap to setup with your lawyer, and helps greatly to seal the deal, as it were, as clients are unwilling to buy systems from you unless your name is Microsoft!
(In other words: What happens if something happens to you? We're stuck with a useless system, cos you are the only one who knows how it works...)