It took me about 5 minutes to setup Pusher and for that I get private channels, presence, someone to handle the scaling etc... as djb_hackernews already mentioned.
We outsource DNS, email, hosting infrastructure, anything I possibly can which isn't core to the product itself.
The question shouldn't be why outsource this, the question is why would it be worth our time writing and supporting it ourselves when we can be working on other things?
Maybe we'll insource this stuff when we're at a point where we hit the 'enterprise' plan on Pusher, when we have a few more developers and a dedicated sys-admin. I'll cross that bride then, in the meantime I'm happy to have a $49/m hit on my credit card and move onto the next thing!
All that aside, it's great to have options so thanks for releasing this!