As a 20+year pc user I am appalled at this controller stuff... but the option should probably be there. There is soo much cross-platforming going on. My 15 year old son would have a torrid time learning a game like this with a keyboard. 
Controllers are significantly better for playing a game on, especially with the move from the crowded computer desk in the corner, to having the PC on your 'TV' screen and sitting on a couch, relaxing, chilling and enjoying a few games. So I am typing this on a comfortable couch, the browser is on a 50inch Plasma screen, feet up, and a movable table with a wireless keyboard on so I can type. It sits comfortably in my hand, I am not couching or bending over with face near the screen like it used to be in the olden days. Not really an age thing either, as I am 20+ year as well with my first gaming experience being the Commodore 64.
Problem with controllers is that there was never much native support for them. They always somewhat existed in some fashion but quite a number of games were better with mouse-pinpoint accuracy and this is where the Computer-game market was, RTS, FPS, etc. Platformers, Adventure titles, Fighting games, all came out on the console and were more popular there.
What has happened in the past years that the Computer-Game almost died, it was really on its death-bed due to the rampant issue of piracy and big publishers only releasing the big name titles on the consoles. This resulted in a paradigm shift when these games came to the PC, they came with controller support too and biggest push here was by Microsoft with the Xbox360 controller (which is pretty much the best one too). So a great number of titles ended up supported, there was a 'standard model' and more companies followed suit.
The main reappearance of PC gaming is a result of Steam, done by Valve. They promoted a framework/system which did no rely on horrible having your CD-disk in the drives (which got scratched and broken), easy to keep up to date, and a communication platform and system making multiplayer between you and your friends far easier. One of its biggest successes are the 'sales' revitalising the PC market as people were willing to pay prices which undercut console options.
So whilst controllers tend to fall short in pinpoint-gameplay which the Steam-Controller is meant to be resolving, it does offer a better playing experience overall in my opinion.