Yes, that's a big one, although I must say I've been pleasantly surprised by the big supermarkets online service here in the UK. The Tesco and Asda websites are not exactly usability masterpieces but they are pretty good.
At least http://Tesco.com has the gallery sliders so you can browse. http://vons.com makes you drill down through endless, nebulous taxonomies. The browsing method of shopping that we are accustomed to isn't being satisfied. I just want to navigate to the produce section and see images of all the produce.
I agree. A lot can be improved there. The reason I'm not touching this is that a few big boys have complete control over actually selling those things affordably. I haven't looked into it much, but if my users can't fill a basket full of things and checkout at one of the stores, it won't be very useful.
I find the Ocado website (and mobile app) quite good. Their service is also excellent.
Yes, they are really good but more expensive than the others.