The site relies on [X]HTML to present content, so you can use a subset of HTML tags to format your post. Please note that we've tried to provide flexibility while restricting the possibility for abuse. While we don't have a lot of trouble, we ocassionally get invaded by a troll or two and then have to regrettably lock things down a little tighter.
So, to answer your first question, VSarkiss edited his reply, added <strike> tags to the text he felt was no longer needed, added the additional text, and then used <STRONG> tags1 to highlight the word Update.
(By the way, that's a local convention we use to indicate that we've edited our posts, either by adding additional information or by removing stuff that's no longer relevant. The idea being to let people know that's things have changed and that it might be worth re-reading the node.)
We appreciate any contributions that folks are willing to make. There are a few of us trying to keep the site up to date. We would rather folks slouch about for a time, get their sea legs so to speak, and then think about the contributions they can bring to the table. We're a varied and talented bunch and we fully appreciate the unique contributions that people are willing to offer. It's part of the ethic of the place, one I've personally found very rewarding.
As far as the inconsistent formatting tips go, well, that's part of the evolutionary process. You may have noticed that more than 200,000 nodes have been posted since the Gates were first flung wide. That's a lot of content to keep clean. Again, we're trying to get the job done, but it's mostly a volunteer effort, so things get done when they get done.
Some of the material predates the current suggestions from the W3C. That's why you'll see different suggestions. Personally, I prefer to see people use <P>...</P> tags to mark their paragraphs, but it's a question of style in some respect.
We are working to make the site more XML compliant, so we've asked people to begin being more aware of XML strictness in their markup, e.g. <BR /> instead of <BR>. While it's not fully clear what (if any) impact this will have on future site changes, it seems prudent to reduce the possibility of time-consuming changes should the data need to be converted at some point.
Finally, a Reputation of zero means you haven't earned any experience yet. That'll change as you participate and the basics are covered here.
I would recommend checking out the Tutorial section VSarkiss struck through, as well as this most excellent home node. There's a wealth of material covering the local culture and preferred operating style. It will also provide insight into the mindset and history of the site. It may even answer some of your questions in more detail.
1 - Update: Replaced reference to <B> tags with more accurate reference to <STRONG> tags, after VSarkiss gently corrected my mistake via /msg. Thanks!