EU and Russia have significant trade; EU and Ukraine don't have anywhere that much - and in light of destruction of Ukrainian economy the trade has to become one-sided. "Nothing personal, " as the villain often says as he dispatches an inconvenient man. EU is willing to use Ukraine as a reason to push trade sanctions that may have their own value to EU. But EU will never go to war for Ukraine, and EU will not even risk their own interests in a purely political battle. Ukraine simply doesn't have much to offer EU in exchange for all the losses that EU is already taking in.
This delay (until 2016) in implementation of the agreement means that the current government in Kiev will most likely not survive until then. It may not even survive this winter. This is all part of the plan, however cynical it may look like (because it is.) EU only wants to deal with a strongman who really is in control. The current team in Kiev is not even close to that.