Developer package: "ownership"

So i am looking into purchasing the famous THESIS theme. I notice that no where on their site do they have a “contact us” that I can find anyway. . I’m thinking it makes more sense to go with the “developer’s package” as I hope to help others build their thesis theme sites, but I’m wondering if it behooves me. The question is, if if set up a client’s domain and hosting package myself in my name can I use my developers’ thesis on those sites or is that considered a licensing no no? I’m not trying to be uncool, I’m just wondering why it would be called a developer’s package if I can’t use it as a developer setting up more than one site. How many sites can one person need afterall? I’m guessing the answer is that each client needs to purchase their own copy, (which is fine), just wondering if it still behooves me in any way to have a “developer’s” package. Does that make sense?