Probably just because it's the SF Gate (same reason the only comparison made was to Berkeley).
* Financial aid does not cover housing during the summer because Stanford undergrad is not in session during the summer
* Seeing how Stanford covers tuition and all the expenses for low-income students it's actually cheaper to go to Stanford than to stay at home. It's vastly harder for middle-income families to afford full cost of Stanford, than it is for low-income. Welcome to the modern elite college price discrimination/income redistribution.
* having a car for an undergrad is unnecessary and uncommon in Stanford (it's a large and self-sufficient campus), it's a luxury or cost of doing business if you have an off-campus job.
* there are good opportunities for low-income students got make a little extra money. Taking out a bit more in federally subsidized loans (reasonable if you expect your income to increase past college) and subsidized on-campus jobs which pay more than most post-undergraduate starting salaries would be good options.
* so on, so on ...
The lower-than-Berkeley Pell grant percentage is interesting. In addition to irrational belief that Stanford is "school for rich kids" I'd also point to the following rational reasons:
* Stanford is more selective. You get drastically fewer poor kids as you move to the right of the bell curve.
* Stanford practices affirmative action based on race. Berkeley is prohibited by law from using race and does it based on socio-economic status. Meaning that relatively to Berkeley Stanford discriminates against poor kids to free up space for protected minorities.
What is the defining range of "low-income student" in this statement of yours, and in your several other comments in which you refer to other students? What is the boundary line between "low-income" and "middle-income" in your second bullet point?