It's extremely common to swap out major components without changing the name and number the router is advertised under, but in every instance I'm aware of there was a version number that was incremented on the packaging, eg. WRT54G v4.0 to v5.0 halved the memory (and v7.0 switched from Broadcom to Atheros and v7.2 switched back). It doesn't really help if you're buying online, but if you're buying from a brick-and-mortar store you can pretty much always know what you're getting if you read the fine print.
