I agree with Karin, places like Topshop aren't selective with vintage.. which is understandable I suppose as they know their target market, which isn't necessarily going to be spending the big bucks on quality pieces say, pre-60s. I CAN'T STAND places like that, to me they cheapen the idea of vintage, and saturate the market with basically tat.
I ranted on about this in a previous thread, but I'm gonna go for it again; The word 'vintage' is starting to get associated with either 1. any old crap 2. generically retro, vintage-inspired modern clothing that you find in Primark or Hennes, that is blurring people's understanding of 'vintage'... So many listings I've seen on ebay etc. that are listed under Vintage, and similarly in the seller's description, are modern from the high street.
We were also discussing in that thread Asos Marketplace's horrendous selection of '1940s' dresses, that are actually polyester '70s nightmares.. the regular high-street and trend shopper perhaps isn't going to know the difference, and maybe the sellers don't either!
Vintage is super trendy at the moment and I can't see it becoming unpopular, so I imagine more stores would be willing to incorporate it into their space in the future- Liberty's has opened up a vint. department, have you checked that out? It might be good for you to compare and contrast the Topshop selection with Liberty, which has glorious high end 'proper' vintage.. although at proper prices too!
One of the original vintage collections at Topshop was supplied by Peekaboo Vintage, who I believe describe it now as their 'concession' shop.. They've since opened a stand-alone store in Ganton st with a more discerning boutique selection of garments. I actually found a gorgeous 1940s day dress from the TS concession, mis-dated as late '50s so actually a bit of a bargain.. never seen anything as good since!
I think it's important to bear in mind that these stores want to stock pieces that will echo the feel of their other departments, that compliment the current stock- I do a fashion fair every month with pieces from the 30s-70s and find that the sellers with 70s-90s garments at a cheaper price do pretty well, as the clothing can be integrated into their wardrobes without upsetting it's existing style, if you get what I mean. They can have the whole "I'm wearing vintage you know" thing without really putting any effort into it ;)
It's so popular and 'in vogue' right now that everyone is wanting to get in on the action, even well-known vintage retailers like Beyond Retro and Rokit so rarely have anything of interest to the people I know that wear vintage, but they're like the go-to stores for regular shoppers who want what they consider to be vintage.
... I sound a snob. I don't care! :p