Lusthaben, I think you've probably hit the nail on the head.
But, and this just my 2c worth, I suspect Vox' approach is very much historical, going back to when modeling was newer and there was a 'divide' between modeling manufacturers (I think Line 6 was the first to bring out a modeling amp) & traditional amp manufacturers.
Nowadays modeling is very firmly established and its all intermingled by which I mean that modeling companies like Line 6 are now using valves, teaming up with Bogner, and 'traditional' amp manufacturers are now big on modeling to run side-by-side with traditional valve products.
Vox, Fender (Mustang), Peavey (Vypyr), Laney (Prism), Highes & Kettner (Zentera, Zen Amp) are all examples of the latter. So I don't think this is as sensitive an issue as it once was - & if Line 6 who market globally (& AxeFX) haven't been sued by anyone for disclosing the amps and effects being modelled, I really don't think this over cautious cloak & dagger approach needs to be continued.
In any event, the descriptions used by Vox (as an example) are largely (albeit not always) a giveaway - so you could argue that those descriptions on their own are enough to cause a copy-right issue anyway!
So, with no-one being sued after all these years I think it's time for companies to stop being frightened by their paranoid lawyers - and as long its clear that all you're doing is modeling the amp & not creating a real live version to sell, I really can't see why there is still a reluctance to quote the amp or effect being modelled.
Even Behringer, renowned for (shall we charitably say) being 'imaginatively re-inventive' in their product approach (where any similarity to other products on the market is of course wholly accidental!) have never been successfully sued for any alleged copy-right breach!
Anyway, reinforcing Lusthabens observation, surely manufacturers should be flattered that their products are worthy of being modelled. I mean, what great cross marketing - a Fender Mustang user buys an AC30 because he loves the AC30 tone & wants the real thing (or vice-a-versa with a Valvetronix owner to a Fender Bassman etc). As I said, it's all intermingled now.