Mac OS X is the name. 10.x.x is the version number. You kinda have to do something when you get to version 10, because after that things start to sound awkward. I mean, doesn't Photoshop CS5 sound so much better than Photoshop 12?

Shit on the internet is single-spaced because of how HTML has to handle white space, not because of deliberate choice on the part of the authors. Because markup is indented and formatted for readability, browsers have to treat white space specially, lest the text on the pages you read retain multi-level indenting from code formatting. That said, I was taught to use two spaces, but one just makes more sense to me.

You could have entered tons of spaces after that period. Depending on which comment post mode you're using, it may be using standard HTML behavior, which strips out superfluous white space, including double spaces between sentences.

In before the Ad Block Plus comment.