Most people posting on this board are probably in the 25 or 28% marginal tax bracket. In addition, long term capital gains are taxed (usually) at 15%. Therefore by not holding long term, a year, you would only be concerned whether your investment increased 10 - 13%, not 30%. I would think that most good traders feel they can make up this 10-13% difference by making good use of their money.

The 28% bracket goes up to $182,800 of TAXABLE (not gross) income. After that it jumps to 33%.