They don't give interviews to just anyone who applies. IIRC the first time I joined (2009, interviewed in late 2008) the stat was that ~2.3 million people had applied to Google, ~1000 had been hired that year, and your odds of getting in were like 2000:1. There were pretty well-known tricks for getting past the initial resume screen, like getting a referral, having an Ivy League degree, having a hot tech company on your resume, or coming through a recruiting avenue (eg. GSoC or TopCoder) that Google sponsored.
Maybe the interview:applicant ratio is better now that there's ~100K engineers rather than ~8K engineers, but a quick back of the envelope calculation indicates it's still likely not everyone that applies. On my team last year (before the hiring freeze) maybe ~20% of engineers do interviews regularly (a bit better than it was in ~2010), and we'd usually limit it to 1/week. That's ~20K interviewers * 50 interviews = 1M interviews/year, which is definitely better odds than in 2008, but still nowhere near enough to interview everyone who applies even if the number of applicants hasn't grown at all since 2008.
Maybe the interview:applicant ratio is better now that there's ~100K engineers rather than ~8K engineers, but a quick back of the envelope calculation indicates it's still likely not everyone that applies. On my team last year (before the hiring freeze) maybe ~20% of engineers do interviews regularly (a bit better than it was in ~2010), and we'd usually limit it to 1/week. That's ~20K interviewers * 50 interviews = 1M interviews/year, which is definitely better odds than in 2008, but still nowhere near enough to interview everyone who applies even if the number of applicants hasn't grown at all since 2008.