I'm speaking hypothetically, as if holding inventory wasn't an issue.
For most eStores, inventory *is* an issue. If it weren't, I'd set up eShops based on Amazon's product catalog. Offer it all(!), if you don't need to carry inventory.
But since "inventory" is one of those "necessary evils", it's like what piatkow said. It's a balance between taxable inventory, cash flow, and fulfillment delay. This applies regardless of the fulfillment center location: your basement, back-of-store, Amazon warehouse, or the manufacturers assembly line.
Hypothetically-speaking, every shopper wants the Deal, the lowest price, delivered this afternoon, with 365-day free returns. In reality, you try to offer the best value for shoppers, and maybe make a buck along the way.
is it better to have a more curated shop or to overwhelm the customer with options?
I know what "curated" means in 2012, and I'm not sure if that's the proper adjective to use for the product catalog for an eShop. A well-formed product catalog takes constant attention, continuous improvement, and an effort measured in man-years to keep relevant. It means having the proper weights, dimensions, related products, accessories, shipping restrictions, inventory, reorder points, and restock levels in place for each SKU. This level of detail can't be achieved via "curation".
A well-designed eShop will have what the customer is looking for, at a fair price, with accurate shipping rates (both domestic and international). If the eShop offers more selection, it needs excellent product filters to help narrow choices.
Customers need to be able to find what the're looking for *on your site*. Like what dpd1 said, "great selection" is never a bad thing. The key is to offer search tools that allow the customer to find a category, drill down to products, then filter those products based on attributes contained in the product catalog: Size, color, manufacturer, availability, price, etc.