Interesting, when I bought SH3 from the Ubi online store, I paid and downloaded everything immediately. Same thing with SH4.
That was a year and a half ago for SH3, way less than that for SH4. But I think they have a "new" Ubi store since then, I remember getting an email about their "new and improved" site.
Sounds like they went with the new and left out the improved part.
Edit: altho I paid by credit card, maybe it had something to do with using Paypal. Do they require a waiting period to make sure the payment goes through okay? I don't use Paypal so I'm not sure if that would even be justified.