However, would you please stop assuming that similar means exactly the same!?! You do not farm and level up Kerrigan mid-level, you use her to help attack and gain new abilities between levels, however mid-level you will stay the same.
On the Yetis, people do not seem to want to pay attention to the words that go along with the screenshots. You kill the Yetis to gain DNA so your entire army can resist the flash freezes. It has nothing to do with leveling up Kerrigan, at least not in any way that is different than the rest of your army.
Again, unless you have solid proof, a 100% fact statement from Blizzard saying that this is what they are doing, STOP COMPARING IT TO WARCRAFT!!!!
Also, it was their whole plan to make the HotS campaign different from the WoL campaign, in more than just changing from Terran to Zerg. If you can't handle that, or want to complain about everything like pretty much everyone else on these forums, then at least have the decency to accept what you know you cannot change.
All of your crying is pointless, and is falling only on the deaf ears of those who feel the same way. Vocal minorities feel like the majority on the Forums, simply because most people go to these forums to join the vocal minority, i.e. to complain about things they can't change, and don't want to accept.