DSP website gives no indication of sale being on exclusive licence or whatever, and as Nametower says it is common to see entire sites inc DSP for sale.
DSP has also been offered for sale on several of the forums which are visited by RJ (the designer of DSP) and I do not recall him ever challenging a sale.
Maybe a PM to RJ will clarify before Nametower buys, if he feels that would be the best course of action to protect his purchase.