This makes me think you don't really understand the issue. It isn't that you're forced to withdraw or spend more than you want to--it's that you may not be able to withdraw as much as you need.
Yes, you are right that if your 401k is your only source of income, then 72(t) will not be a good choice for someone retiring really early.
I wrongly assumed that most early retirees would be in a position similar to mine, where I have several accounts and sources of income, not just a 401k.
However, with a currently maximum allowable contribution of only 17k a year in a 401k, I'm wondering how someone can even retire at age 30 with this being the only source of income (even if there was no early withdrawal penalty).
I did the math, and someone who starts contributing the maximum to his 401k as early as 20 years-old (something that few people do at this age) will have only about 213k at age 30 (assuming an average 5% compounded annually, and only 17k contribution/yr. with no raise to the contribution level).
You're going to have to live pretty tight for this money to last another 60 years!
For the most part, I think you're right - it would be difficult to get enough to just use 401k alone.
However, take this scenario:
$70,000 average income over 10 years.
Employer matches 100% up to 6% = $21,000 / yr contributions w/ 5% growth = $260,000 in 401k
Add in $5,000 in roth IRA = $60,000
Add in a $100,000 paid for house ($1,000/mo monthly payment on a 10 year loan at 5%).
$320,000 * 4% SWR = $1,000/mo expenses with no house payment
Obviously this isn't 100% 401k, but with only $50,000 in roth contributions that can come out penalty free over 30 years, that's only $140/mo. I doubt the 72 on $260,000 would give you the other $860/mo - probably more like half that if it allows a 2% withdrawal rate.