Of course, you could also say...
> A lot of fast growing start ups are terrible places to work, because of the very virtue of what they are.
The size of a company has a little to do with its culture. Amazon, Apple, and Microsoft all employ over 80,000 people, but have very different cultures.
I have seen some start-ups which have awful cultures, with terrible morale problems. It is really not the size of / number of employees at a company that defines its culture, but the mindset of the people in charge.
They are small, have lots of money, there is no bureaucracy and there are no managers getting in their way of achieving great things.
Microsoft has 95K+ employees and has by and large turned into IBM. Google has 45K+ employees and is rapidly transforming into the next Microsoft.