Experience is worth a tremendous amount in this industry, but you'd never realize this if you're too loyal to a single employer. Shop around, hop when it benefits you.
Most starting new-grad packages are around $100K these days in the Bay Area, and said companies would be content giving you 1% to 3% raises a year from there. To maximize your value you must change jobs.
Outside of mobile/web dev?
1) True, if it had been his own firm, he would have been a millionaire. But would he have known enough about his business at age 23 to create that same firm? I'm betting he has learned a huge amount in the last two years -- that he's much wiser and more savvy now than he was before he started this process. That wisdom will make him much better positioned to someday build his own empire than he would have been had he jumped the gun and started building without it. That's an advantage that very few 25-year-olds have.
2) OK, so his boss is a millionaire and he isn't. But what he will find as he earns more money is that there is no amount of money that is "enough." Say he goes out on his own and makes as much as his current boss does. Now he's a millionaire, but now he finds himself envious of multi-millionaires. And what he doesn't realize is that those multi-millionaires are envious of people who have hundreds of millions, and the people with hundreds of millions are envious of the people with billions... and on and on. It never ends. There is never enough.
Or as one of my favorite reads, Stephen Mitchell's translation of the Tao Te Ching (http://acc6.its.brooklyn.cuny.edu/~phalsall/texts/taote-v3.h...), puts it:
Fill your bowl to the brim
and it will spill.
Keep sharpening your knife
and it will blunt.
Chase after money and security
and your heart will never unclench.
Care about people's approval
and you will be their prisoner.
Do your work, then step back.
The only path to serenity.