Quite right, but simultaneously the demand and affordability of smartphones in Asian market is in increasing curve, and it will continue for next few years, so there is enough vacuum for new competitors and existing both.
What Mediatek has accomplished in this case is to win a solid share of the market in Asia, then move to other geographical areas with time. They are in a pretty good poisiton, but there is no shortage of competitors out there for them to vie against.
Mediatek will be a more successful as compared to the first two giants in Asian markets, as Asian phone market is booming these days and every android phone is shipping with MT chipsets. And these phone is in huge demand as Chinese manufacturers are being able to sale at a very competitive price as compared to Samsung, Apple, HTC and Sony.
It's shaping up to be quite a horserace behind Apple in this market segment. The key is who will ship 64-bit ARM-based SOCs and when. That kind of low-power RISC architecture is paving the way for smaller companies to take aim at the established giants in the processor market.