Everytime I see your point made, I want to remind others that the execs don't have to exercise and sell when their options are about to expire (usually at ten years and one day). They could, instead, exercise and hold especially if they believe the price is going up.
I'm not sure I buy into the tax purpose reason. These option exercises along with their incomes already place them into the highest tax bracket. So, I'm not sure how selling their options one year helps them tax-wise year to year.
IMO, the company places a large portion of total comp in stock options and the execs are exercising and selling for annual income purposes. If they believe that the price was going to shoot up bigtime in the near term, they'd exercise and hold. Otherwise they are merely keeping their income at consistent levels. JMHO, of course, as each exec probably has his/her own personal reasons.