How is $1 salary justified to IRS? There are a bunch of executives who have $1 salary [0], including Mark Zuckerberg. I really doubt it's considered reasonable.
You don't have to justify low salaries to the IRS conceptually, you just can't use them to avoid paying payroll taxes.
I would assume that companies like Apple and Facebook have competent tax teams that make sure their obligations are fulfilled, even if that means paying payroll taxes on a portion of the stock-based compensation to their executives.
What they report to the IRS and what they show on financials could be 2 totally different things. Entirely possible that they are paying taxes on a higher salary.
Base Salary is just a tiny component of an executive's salary. It is a PR move. Executive salary is made up of Cash component (which includes Base Salary & Bonuses), & Equity.
Equity constitutes towards almost 99 percent of an exec's salary. There are short term equity plans and long term equity plans. The equity payouts are generally in millions.
Companies have to release a DEF14A (30-40 pages) each year to show Shareholder's how much the Top5 Execs were paid each year.
[0] http://en.wikipedia.org/wiki/One-dollar_salary