They can't effectively resupply the troops in the airport, and the rebels have a steady stream of supplies coming from Russia. As long as fighting continued, it really was a matter of time. The question is how much this can heat up without the negative OSCE observer reports forcing the EU into action again. There are unconfirmed rumors that the rebels are going to or are currently breaking the cease-fire because they want to take all of Lugansk and Donbass, or as much as they can. As is Ukraine is basically shutting down and blocking off the rebel regions completely, essentially treating them as a hostile foreign country rather then as one of their own provinces in revolt. I wouldn't be surprised if the rebels don't want the conflict to settle along those lines.
I came across a theory that Russia is using the conflict in Ukraine as an opportunity to combat test some of their new and shiny gear. I think we can say that this is correct. Fragments of what could be a missile from the Pantsyr were found in the conflict zone, Kornet-M ATGM tubes, possible traces of another advanced ATGM (the Hermes), indirect evidence of the use of guided artillery and mortar shells, massive and widespread use of UAVs, etc.
It's used to refer to the Ukrainian troops that held the portions of the Donetsk airport that are still in Ukrainian hands. It's intended as a compliment, implying that what they did there was superhuman.
