I'm wondering what the OP (or anyone else) thinks that the illegitimate reasons for still using VB6 might be. I guess the only one that I can really think of that might fall into that category is that they hate VB.NET on principle because they want(ed) Microsoft to produce a COM-based VB7 and beyond. There are undoubtedly such people and I think that that is silly but, even then, it's a person's own choice what language they use so I still don't think that it would be fair to call that an illegitimate reason.

Before a storm of VB6 vs VB.NET hate whips up, just let me say that I'm not claiming that you can't make reasoned arguments in favour of VB6 over VB.NET; just that some people are really interested in reason on the subject and really do just hate on principle. There are also those who combine the two.