It's not even costing them $100,000 to do this. What does $100 of service cost linode- probably very little. That's about 4 months worth of the basic hosting plan, which is 1/40 of a server (so their FAQ says). The cost to linode for this promotion is probably much lower.

This doubly makes me wish they offered this to existing customers buying new nodes, however it's extremely similar to the Amazon deal a few weeks back.