I think that has to do with Dahon having more high-end options than Oyama.
When comparing low-end, budget options between Oyama and Dahon, like you said Oyama's value for money cannot be matched.
Their bikes have better specs for less money.
But like I said in an earlier post the quality isn't necessarily lower.
I do not know about high-end models because I haven't tried any yet. Soon...