not sure which distro is dominant on scaled projects but Ubuntu gets plenty of use on large projects too - from the article:
"Global enterprises including AT&T, Bharti, Bouygues Telecom, British Telecom, China Telecom, China Unicom, Cogent Communications, Comcast, Deutsche Telekom, Korea Telecom, NEC, NTT, Numergy, Orange France, Time Warner Cable, Turk Telecom, Verizon and Yandex, as well as leading web scale services such as Netflix, Instagram, Hipchat and Quora are all building next generation services on Ubuntu"
"Article" is one word for it, a more specific phrase would be "press release".
It's hard to tell from these lists how seriously a lot of those companies are relying on Ubuntu. Obviously some are (HP for example). But I've seen my own employers listed in press releases where us implementors were wondering "do we really still use that stuff? Oh yeah I think there may be a box or two still running that from when we were testing the waters."
As far as I have seen it's actually dominant in general. The only stats I found[1] say it is totally dominant in EC2 deployments (55% of the total with second place with 24% being a generic "linux").
RedHat has carved out a huge chunk of the in between space. RedHat sells to people who buy support contracts. Some guy running a personal email server doesn't have the money and the likes of Netflix doesn't need it because they have the expertise in-house. You see a lot of RedHat in corporate IT departments.