Personally, I don't think stricter scrutiny (which certainly does occur) is the main reason for the long and slow lines for foreigners.

The real cause is understaffing. Why?

Foreigners can't vote. They've got no say.

They are treated like slaves, subject totally to the whim and convenience of their master. Held in uncomfortable quarters. Herded from place to place. Kept in the dark about what is happening to them. Made to play the supplicant, in constant fear of bringing upon themselves, by unguarded word or deed, arbitrary judgments and penalties.

So what, if foreigners have to wiat two hours in line? Nothing they do can affect the passport control staff.

No wonder we have to resort to guerilla warfare ...

(from the Airline Passenger's Guerilla Handbook)