Altman's post suggests that the context needs changing. I suspect it needs changing to keep up with some of the very changes YC has wrought - changes to VC and the creation of startups and the options available to the sorts of employees startup founders need.
The issue is that the new startup culture has diversified power and our concept of 'business founder' is out of date. A software company founder is not the analog of a white shoe law firm partner. A personal realtionship with Jeff Bezos isn't why people buy toasters from Amazon or host their SAS on AWS, because it's not some Rolodex full of 30 year of golf course relationships and keeping the jobs of bureaucrats secure that make it rain. "On the internet nobody knows you're a dog.* [1] Or cares that you're a founder.
While I agree with Altman that something needs to change in the direction of making employee's richer ,I think he probably doesn't go far enough. The problem isn't so much tax code as capital structure and the rigidity of company structure that results.
A key hire is a key hire because it changes the company. Ideally, a company would change it's structure to reflect that change. Ideally, a company's capital and corporate structures would be agile as in development.
Key employees are just as exposed to the 'you can be a founder' meme as everyone else, and they're in a better position to pursue it than most. A founder shouldn't expect talent to hang around making them rich. In terms of game theory, I think of it as a founder's dilemma. Altman's piece suggests YC might be seeing it too.
In the current context, a founders's 30% of a $40,000,000 exit is better than even a 1% employe share of a $1,000,000,000 one - much better perhaps than the numbers would suggest because 30% gets a seat at the table, and that old Mark Cuban idea of looking around the table? Well if you're not at the table, the worst case is you're just dead money picking up the tab for someone's boat payment.
[1] http://www.paulgraham.com/hiring.html