Not having to download a blockchain enables people that only have 50 kb/s connections to use it. Or even 4 kb/s connection.
Paypal doesn't require a blockchain. Neither does MintChip as far as I can tell. What's the point though?
I would also point out Bitcoin with a lite client (or ewallet service) doesn't need to download the blockchain either.
Not having to download the blockchain is OPTIONAL in Bitcoin depending on how much trust you need.
I doubt any major merchant wants to run their wallet without access to the raw blockchain though.