[sajidnizami]

They are part of Bizspark program so they got free licenses. They don't even have much hardware.

Important part isn't caching. You can just create HTML copies off a page and serve them through a fast server, that is a very easy cache.

Difficult part is smart caching, cache getting updated when they need to be and persisted properly to the DB. These guys have nailed it in my opinion.

I often lookup these guys and optimize my own sites and have been following them since their beta phase.