It's a conscious business decision they have made, you can do whatever you want to with your business. As long as it looks right in all browser/os configurations I don't think your customers will mind.

It's OK for anyone to do anything they want with standards, you can ignore them or follow them at your pleasure.

Whether or not you decide to ignore standards - there may or may not be consequences. And if there are consequences, you still might have perfectly valid reasons for accepting those risks.

For a long time, arguably even till now, Microsoft didn't pay enough attention to web standards. They made a business decision for whatever reasons which is their perogative. One of the consequences is that they've lost a lot of browser market share. Whether that matters to them or not I don't know.

I suspect that Google balanced the benefits and harms of strict adherence to HTML and CSS standards and found that, for that page at least, it would be much worse to be anal about standards and the impact to the user, if they didn't meet the standards, would be pretty much nil.

Makes sense to me.