Wrong information.
I think they can handle this they need to manage a large amount of wallets.
I dont kow but maybe simplewallet's or bitmonerod's APIs have a function for creating new wallets.
Well, Poloniex does not manage a large number of wallets. They have one address and manage a large number of payment ID's which is the purpose of TheKoziTwo's script above.
Maybe there is a new way of doing it with the recent commits by Moneromoo but its still new stuff.
It's in current head now (#317), so I guess it's a matter of getting it out there (MyMonero adding support as well would be nice).
You may want to take a look at this and search for "poloniex" : https://www.reddit.com/r/Monero/comments/2gi4zb/the_monero_missives_weekly_report_september_16th/
td;dr they use get_bulk_payments :