Idem

The only time I use is a cookie for identifying the user.
There are more options to do with a db. If you like it or not.
But most companies like to get stats(mostley the sales).

Shopping has all to do with marketing. And nice graf's and charts displaying
all kinds of information... And this information is also important.

Off cource in some smaller cases this isn't really needed. But nontheless it's the best solution!

Actually my firm is specialized in making these kind of websites. For small and large companies.
We build stores, shopping-carts etc... The best is to make a custom one e.g. build one that's got a good engine
and customize it for each customer.