We are considering adding this, but it's going to require quite a bit of work and so it's probably not going to be finished anytime in the near future.
You should absolutely feel free to purchase them on the author's site directly via PayPal if that option is available and you prefer it -- we really don't keep very much beyond payment fees from 3rd party Marketplace sales, anyway; the vast majority goes directly to the authors.
Anyway, it's a good suggestion, and one we've been given several times since the Marketplace opened, so we're not dismissing it, just being upfront about the likelihood that it's going to be finished in the next week :-)
