[mtomczak]

There are similarities between Facebook and AOL. But one significant difference is the interface. AOL had a proprietary client to access its service network. It made sense at the time, but it was often clunky, had not-insignificant bugs, and generally behaved like an application separate from the rest of my user experience. The client also wasn't nearly as ubiquitous as a web browser (though AOL CD's were so common that we used them as coasters and frisbees).

Facebook itself may be a closed network, but it's a closed network running in an open client---my web browser, which works on all my computers and my cellphone. Since the Facebook team doesn't have to build the end-user software, they can focus on their core competencies of the network and the user experience inside the browser. That takes a lot of the complexity off of them that AOL had to embrace (in my experience, the Mac client was never as reliable as the Windows client, for example).

Facebook could go into the business of making its own client apparatus (such as a branded phone), but why bother? The web is serving quite well for them as a transport medium. I think that AOL suffered badly when the state of the internet became "There are these closed networks, and then there is everything else, and you need two end-user clients to access the two separate systems." As walled-in as facebook is, I still use the same client to access it as I use to access the rest of the web, and hyperlinks inside facebook and the larger web can still interoperate between each other seamlessly. That's an architectural strength that AOL didn't get to leverage.