Is there really any value in having the source code for custom modules? 

Would it really help to have source code if the developer went away and the next version of DNN broke it?  Wouldn’t it be cheaper to buy a different one to replace it?

I definitely agree with Robert.  I think it is important for the success of DNN for module users not to have the risk of the creator of that module suddenly stop developing it and no longer supporting it.  This is a fear for many larger companies as they see using modules from the DNN community as a risk because they these development 'companies' tend to often be one or two people, sometimes with other jobs, and so the chance of this happening is great.  Often times, even when a company does not offer its software, a company using it may require them to escrow it somewhere so that in the event they do stop supporting it or get hit by bus, the company will not be left stranded.

Besides that, one of the values of DNN and open source in general is that it allows you to get a ~80% with baseline functionality, which allows you to be able to provide a very custom tailored solution for yourself or someone else by only having to focus on the last 20%.  One solution cannot work for everyone, so being able to take the source and tweak it for your own use is one of the value propositions of DNN, so I think the more 3rd party module developers that offer their source the better.