Qualcomm is currently the market leader in the mobile chip market, and they've chosen a different strategy from Nvidia with its quad core processor, but even compared to Samsung, Huawei and Apple, which also are planning to ship devices with a quad core 1.5 Ghz processor. And I can't say I blame them, because I actually think they are right for the most part.
Qualcomm has changed their CPU architecture, bringing performance improvements of around 40% over Cortex A9 per core, so a dual core 1.5 Ghz based on Krait, should be 40% faster in most situations than a dual core 1.5 Ghz Cortex A9 processor. The question is, will it be faster than a quad core 1.5 Ghz Cortex A9 processor, too? I'd say yes, and that's because most applications still don't or can't use multiple cores for maximum efficiency.
At most they leave some low-end tasks to another core, but will still do the heavy lifting with one core. This causes most of the cores in a processor to be unused, which means only the first or first two cores should matter to you performance wise. Since Qualcomm's Krait cores are faster than Nvidia's Cortex A9 core, this means the whole chip should fare better for most applications than the Tegra 3 chip.
Qualcomm says they don't care much about how many cores the processor has, but how the overall performance is, but I think they want the marketing power of saying they have a quad core, too, because they've also just announced a quad core 1.5 Ghz Krait processor, to ship in devices by the end of the year.