DY: The more desirable Chassanim would naturally receive larger dowries. Being that a learning boy is (as a practical reality, without debating why) a more in-demand shidduch, he will get a better dowry. Which in this case effectively translates into a pre-agreed set period of support.
Non-Kollel Chassanim tend to essentially get a dowry in that the Kallah’s family is bearing a much greater burden for the cost of the wedding and perhaps the startup costs to get the couple on their feet. (i.e. in EY it might be an apartment or elsewhere furnishing, etc.)