Yes. PHP does the same thing. Actually, most frameworks do that; very few keep state within the application server between requests. Statelessness, in that respect, improves scalability.
Of course, if you keep that state in memory then you are fucked when you need more than one web app server to handle the load.
I know memcached is very fast. However it's at least an order of magnitude, or more, slower than in memory lookups. Given how simple sticky sessions are I guess I'm not sure why you'd want to incur the overhead of re-buildling your state via external network calls and object serialization/marshalling/etc... for every request, and doing it all backwards at the end of every request.