Namecheap does NOT need to be waiting for even a single confirmation to accept deposits. The kinds of services that they offer are all easily reversible within the kinds of timescales where double spend attacks are feasible (domain registrations take days to clear), so they are certainly not in the class of merchants that could practically be defrauded. The only businesses that actually need to wait for transactions are SatoshiDice, exchanges and consumable digital goods sellers (eg. game codes).

Fortunately, most Bitcoin vendors actually do accept transactions without waiting, and I've only heard of SatoshiDice successfully being defrauded (they've since added various defense mechanisms against unconfirmed transaction double-spending).