"If you’re sane only about 25% or so of your gross income is subject to the results of real estate negotiations. Close to 100% is subject to the results of salary negotiations. Thus, your salary negotiations are probably going to be the most important financial decisions you will ever make."
That's pretty irrelevant really, what's relevent is the difference it can make. First, if you negotiate a 20% discount on the 25% you're doing better than negotiating a 1% pay rise for the 100%. Second, a negotiated salary recurrs annually, it's not a one-off sum. So yes the conclusion is right, but for the wrong reason.
The 25% he alludes to is your recurring mortgage payment, which also happens annually--monthly, actually. What he means here is that a discount of 5% in your mortgage negotiations is much less than an increase of 5% in your salary. So he is right, for the right reason.
corin_ is right - salary is recurring, mortgage/real estate purchase is one-time. You pay off the mortgage with recurring payments, but they are based on the one-time amount. If you negotiate $10k extra salary, after two years you will have $20k extra. If you negotiate $10k lower real estate purchase, after two years you will not have $20k extra. (Technically you will have a little bit more than $10k extra due to compound interest on smaller principal, but nowhere near $20k.)
That's pretty irrelevant really, what's relevent is the difference it can make. First, if you negotiate a 20% discount on the 25% you're doing better than negotiating a 1% pay rise for the 100%. Second, a negotiated salary recurrs annually, it's not a one-off sum. So yes the conclusion is right, but for the wrong reason.