What [White House Press Secretary Tony Snow is] saying is that, yes, expensive health plans would be taxed more. But people would respond to the new policy by scaling back their health plans. Thus they’d avoid the tax.
In a later post, he corrects himself (my italics):
[Snow's] point wasn't that people with expensive health insurance plans would scale them back in response to the president's proposed tax reform. Rather, it was that insurers would offer more coverage for less money. Thus (at least some of) the affected workers would find themselves getting the same coverage and, perhaps, a raise. The value of their compensation to them, after tax, could go up. He has a good point.
Yes, health insurance companies have a longstanding habit of offering more coverage for less money.