Hard Bargain on Pay

I missed this in the Washington Post op-ed section earlier this week, so thanks to Ed O'Keefe for highlighting it: Wisconsin Gov. Scott Walker (R) wrote a piece about the epic battle in his state over collective bargaining rights for public employees. Here's how he led it off:

Imagine the outrage if government workers did not have collective bargaining for wages and benefits. Consider the massive protests that would be staged by labor leaders all across the country.

Think I'm talking about Wisconsin? No, I'm talking about the federal government.

Contrary to what the Obama administration would lead you to believe, most employees of the federal government do not have collective bargaining for wages and benefits. That means the budget reform plan we signed into law in Wisconsin on Friday is more generous than what President Obama offers federal employees.

The right to bargain over pay and benefits is indeed rare in the federal sector, and I can't see that changing any time soon. So why exactly is that deemed acceptable, while many people on the left consider it unthinkable at the state level? Is it the nature of the work (after all, some federal employees, such as postal workers and air traffic controllers, do bargain over pay), a quirk of history -- or is there some other factor at play here?