Those instructions are BS. Flash does not work on 2.1. However, there are several devices that run Flash Lite (it came on my Galaxy S Vibrant, for example). Someone with Flash Lite tried that and thought they had real Flash when really they just had Lite, and it spread for a while before being debunked. Just read the comments on that post.
Edit: According to Lie Ryan's comment below, full flash is compiled for ARMv7 chips, and so won't work on other processors even with 2.2.
Edit 2: Adobe now has a list of devices that run Flash: http://www.adobe.com/flashplatform/certified_devices/