In part I'm paying 40% in tax so if I'm going to buy coffees it's actually more effective to have them provided by the company. But in general, that sort of convenience and benefit is often worth more than the monetary value.
Tea/coffee in the office is very different to a expensive social events, but it's all on a spectrum, and I value some of those things more than the money. I do however earn a good salary, this could well be different for many others.