This is indeed what happens if the option itself (and not just the underlying security) is actively traded. [1] However in that case, when you receive the option, you have taxable income equal to the current FMV of the option (determined by looking at the market). To do the analogous thing with startup options would (a) result in employees getting taxed even earlier and (b) require using Black-Scholes or something to estimate the value of the option, resulting in "income" that is even more divorced from reality than the current status quo.

[1] http://www.irs.gov/publications/p525/ar02.html#en_US_2013_pu...