I'd like to point out that this is not the case for every Silicon Valley start-up: the three start-ups I worked at (CollabNet, Aeluros, Ardatech) were incredibly frugal with money (exception: salaries were competitive).
At one of the companies, the CEO and I took a trip to Safeway to buy soft drinks for customers. When we got back, I walked around the office telling everyone the soft drinks were _not_ for them, only for customers.
At another company, I had to make a compelling presentation to the CTO to buy a $1.5k printer. "The Linux workstations need a PostScript printer!" We bought the printer, but he didn't like parting with the money.
Being frugal doesn't guarantee success: my CollabNet stock was washed out in later rounds, Aeluros had a fair-to-middling exit to Broadcom, and Ardatech had a good exit to Google. But it's good to keep an eye on the money.