Is Carried Interest in the Grey Zone?

In his March 3 NYT column on capital gains, Harvard Professor and Romney Advisor Gregory Mankiw misses the central point in understanding capital gains -- and that is risk.  Professor Mankiw lays out 5 cases to demonstrate the shades of gray in defining what is a capital gain.  He calls the situations murky and they make his head spin.  If he realized that in all 4 examples that are recognized as capital gain situations, the investors took on risk and had no certainty of gain, he could easily delineate capital gains from ordinary income.  In these 4 situations, the investors and entrepreneurs put either capital or their own time and labor (sweat equity as he calls it) at risk.  They could have lost their capital or ended up not being compensated for their work.  Only in the fifth case that is properly characterized as an ordinary income situation was someone employed to perform certain services for a specified amount.  Take on risk, it's capital gains; get paid a certain amount for a specified job, it's ordinary income - that's a simple yardstick that can help him in his next situation.  Investors and entrepreneurs put capital and labor at risk and either gain or loose based on their judgment.  This principle is at the heart of a vibrant, growing economy.  That's why capital investment is encouraged with a lower capital gains tax.  I can't help but think that this article purposely obfuscates the issue about capital gains to put carried interest into the grey zone.  I am not surprised when president Obama who has no economic training or practical business experience is confused about what drives the economy and how carried interest is rightly a capital gain (or loss).  I would not have expected this from Professor Mankiw.  Mitt Romney needs a new advisor.