Having a limitation of 2 merit per post no matter how good and mellifluous the constructiveness of the post is will take away the reward for in-depth response and analysis. It will contra-work with the aim of the Merit system which is to up constructive posting. We shouldn't be stingy about this thing. It's not like it is sending $$ to a live account. It is just an encouragement mechanism.
If it is that good, then it will receive merits from more than one source. Having a maximum for individual rewards slightly reduces the probability of abuses in my opinion.