Employee Stock Purchase Plans

Am I missing something here or are Employee Stock Purchase Plans the best possible investment anyone can do?

http://www.fatwallet.com/forums/finance/1004350/?start=40

"My company's plan is fairly standard. 2 offering periods per year, 15% discount on the lower of the 2 prices (first day of offering period or last day of offering period), can sell immediately (typically takes 3-4 business days once the period ends to have the stock in my account and available to sell.

Here's a sample of the last 2 completed offering periods.

Period / Lower of 2 Prices / Purchase Price with 15% Discount / Sale Price
1-1-09 thru 6-30-09 / $28.42 / $24.16 / $29.10
7-1-09 thru 12-31-09 / $30.94 / $26.30 / $36.32

The 7-1-09 period is the scenario you hope for. The price was lower at the beginning than it was at the end of the period, which equates to a much larger gain."

This guy essentially had a risk free 20% gain in the first period and a 38% return in the second period. Annualize the returns and he's whooping the shit out of pretty much any HF manager with much less risk, pending he sells as soon as he's eligible to. Imagine working for AAPL over the last 10 years and maxing out your ESPP contribution. =]

Now, why do most ESPP's at banks suck? From what I've read most big banks only offer a 5% discount.

A solid ESPP and a 401k match of 5% should be more than enough to turn anyone making over $100,000 per year into a deca-millionaire before retirement, even considering most most ESPP's limit contributions to 10% of your income.