User blog comment:DaNASCAT/Update Your CSS and JavaScript To Speed Up Your Wiki/@comment-166269-20120822233320/@comment-4543183-20120823004935

The advantage of loading CSS with JavaScript is that we can serve multiple CSS files in one request and have them minified, whereas including them in CSS (via @import) creates a synchronous request (meaning that only one can load at a time) for each asset and they will not be minified (larger file size). This does have the downside of styles not loading if JavaScript is somehow disabled, as you mentioned, but in this case a lot of other features of the site wouldn't function either.

The old import functions will still be around for now, but use of them is discouraged because of the issues mentioned in the blog post above.