It's a nice idea, but tricky to do. The difference is that wages and dividends get taxed in the year they happened and capital gains can't even be calculated until you sell an asset, because you don't know the price it's sold at. And capital gains taxes can sometimes be delayed forever (by not selling).

You could mark to market, but it's tricky for investments that aren't liquid. Do you want to pay capital gains tax on your house every year because the market price is supposedly higher? Do you get it back if the market goes down again?