@Guysensei was suggesting that Ethiopia and Al Shabaab were working in league.
It doesn't matter whether Al Shabaab killed the soldiers in Ethiopia or in Somalia, terrorists shouldn't be allowed to exist in anywhere near our region. Why wait until they spread to us and try to infect our peaceful Muslim community with their wahabbi trash??! It's about preventive measures. I will admit that Ethio soldiers have been in Somalia inappropriately during that whole Bush proxy war in '06 and I'm against that involvement but I don't think this situation compares to that, especially since things have intensified.
And Ethiopia may not be completely getting rid of Al Shabaab(for many political and power dynamic related reasons) but they are keeping them under control. I suspect that Al Shabaab knows this and it's the reason why they are more lenient towards Ethiopia because they realize that it is more of a threatening enemy than Somalia is and they're willing to take what they can get (for now).
Also,
@Guysensei
It doesn't matter how "few" soldiers died, do you think they willingly died as part of some sinister plot with Al Shabaab so that Ethiopia can remain in power??
Why don't they attack Ethiopia? I assume that it's about power struggle...they are addressing their immediate interests first and are tactical enough to understand that they need to operate step by step. Not all Somalis think alike and they want their Sharia agenda to dominate by force rather than risk the possibility of losing in a democratic election where they'd actually have to compete. How can they think of frying a big fish when they haven't even cleared the pond in their backyard??