the difference is that at Google the programmers would be working on fun and exciting new things, so it takes a lot longer to get bored with the company...at facebook? What real innovation is there? I mean if you think about it, most of Facebook's features can be written by any programmer.
The features Facebook has any programmer could add to their blog, sure.
However if you were coding the same feature for twitter I'd be surprised if you kept even 5% of the original code. Coding at the scale facebook is at is a completely different ball game.
Anyone can add those features to their blog but not everyone can add them to Facebook.
There was a time when this was the hard part, but at this point the "scale it up" search space has been explored quite effectively by a lot of different groups to the point where the only reason anyone below the "system architect" level would need to know the ins and outs of this particular subject is because the company has a deep-seated NIH syndrome.
Scaling a system to the Google, Facebook, or Twitter level is hard, but getting to half of their size using off the shelf components is not. Getting the rest of the way on this journey is not something that mid-level tool and front-end coders should ever have to deal with. If they do need to know this information then you are doing it wrong...
