no and yes - do you wish all the products in store A to be exactly the same in store B? I mean everything, pricing, pics, quantity available. If yes, then you could use the same database for both stores. Both stores would be identical in the products, the templates could be different.
But if you wish only some of store A products in store B or want some to have a different price, etc then you need to setup the multistore in the manner as it is coded for. It still runs on one database - but there are addtiional entries for each store so you can have the flexibility to manage each store totally.
There has to be a way to key the database to a particular storefront in order to give you the ability to manage each store separately. Or the stores have to be identical in the the products showing. That's what the store selection box is for.
There is a new multi-vendor store aspect coming out in the near future that may give you a solution in a bit different manner.
I do not have a launch date for it.