It was – in the early days – a way of searching for WP powered blogs because you could use Google to find those version strings. That’s all.
There is no data collected or sent.
Now that part is almost usless, but it helps us here. If you have a problem and we go to your site, one thing we will check is the version – and if we can’t find it we have to ask here and that slows things down.
You can remove it though 🙂