No, 'float' is a property - '<table>' or '<td>' are elements. Float has nothing to do with semantics, it's purely presentational.
By marking up content semantically - it's possible to do interesting things with your marked-up content. For instance, content can be scraped more easily and a screen-reader can use elements to make inferences about the make-up of a page's contents. xHTML can be translated to other forms of XML using XSLT - and HTML content can be shared between desktop and mobile devices with just a stylesheet change. Liquid layouts can be utilised and JS can be used to move content dynamically.
There are a huge number of reasons for marking content semantically.
Using a table is a bad solution for anything other than tabular data.