I agree with your sentiment, but I think the advice has some merit in the sense that if you have an offer that might be the difference between life and death of your company, it is probably not the best decision to fight over 5% of equity. Of course, 40% vs. 90% is a different ball of wax.
On another front, I think the best part of the show (I'm a fan) is that it shows how much leverage shifts from investor to entrepreneur when the entrepreneur has built a real company (usually means has sales on the show). In those cases, the investors often fall over themselves and compete giving the entrepreneur a better deal then they came in asking for.
There is a great lesson in there for entrepreneurs to focus on building something valuable first and then raising money. Because when you don't need it to survive, the negotiating leverage and power totally changes.