Valve has a lot more than 50 employees.
The employee question is a little complex, but here's the thing:
According to Valve's Wiki page, these are the numbers it gives:
Employees - 190
Revenue - $70 million (2007)
(By the way, it still falls far short to Nintendo's massive "Microsoft like" amount$)
Now, here's the twist: The author that wrote the Valve Wiki page is counting the combined employees of Valve and all it's other game studios it had bought throughout the years, studios like Turtle Rock and Team Fortress Software. Also, the Wiki info is from 2007, making it at least two years old. For the record, the Valve website states they have "just over 160" people. But the problem with that info also, it's been there for a very long time unchanged, and it does not reflect the heavy layoffs that went on in the video game industry for the past 15 months or so due to the recession.
Anyway, here's the exact Valve corporate data link from ZoomInfo:
http://www.zoominfo.com/Search/CompanyDetail.aspx?CompanyID=40599726&cs=QGCa4CuRo&singleSearchBox=valve&searchSource=basic_left&companyDesc=&companyName=valve&location=By the way, Zoominfo.com is the place where a lot of the news media outlets go to to get their up to date, inside information of companies.
Now, don't get me wrong, I think Valve is a bad-ass, cool as hell gaming company, with a lot of good people working for it. Other than that, Nintendo is just a bigger monster.