You have to take into consideration what kind of workloads lead to throttling. Laptops are usually not used for the kind of tasks that keep a CPU fully loaded for several minutes or hours at a time. People who do use laptops in that manner are a tiny fraction of the market, and when they experience throttling that does not have any bearing on whether the cooling system of an ultrabook is adequate for the kinds of more typical workloads it is actually designed for.

There have been some ultrabook-style designs that offered inadequate cooling even for fairly normal use cases, but that's a separate issue. Mainstream laptops will be designed around mainstream workloads, and heavier workloads will push them to their limits. Better cooling doesn't come free, and if it doesn't benefit mainstream workloads it's unreasonable to expect mainstream laptops to put more emphasis on cooling capabilities.