Firing up a web browser to run a web app is ridiculously easy. Each web app takes little extra resource on the netbook client.
Installing Windows on top of Linux is a lot of work - buy a licensed copy of Windows (£140/$200+ in UK for XP Pro, via eBay sellers only as it's end-of-life), install it, get it activated by Microsoft (which can involve a phone call), install required Windows updates, then install antivirus, antispyware, personal firewall, Firefox, etc, etc. You need at least 1 GB spare to run XP comfortably with multiple apps, or 512 MB for a single main app.
There really isn't any comparison here.
You don't actually have to use the Gmail account required for Android, it seems, and forks of Android are legal. Removing XP product activation is illegal of course.