Thank you JBB, but...

Well you got it backwards. UX talk was about not making the mistake and start your web page dev from the designer's view: pretty pictures, rounded corners, funky shades, coded effects.

It was about starting your web page dev from the very basic semantics aspect, relying on just what basic html is about: content wrapped in proper tags linked by anchors. All this keeping in mind two aspects: visual aspect is just a possible scenario you need to account for, images have also to be content, otherwise they have no place in HTML but in CSS.

Then, if you are a good web dev, you will understand to provide progressive enhancement and graceful degradation of your web page, exactly for the reasons you mentioned:
The average internet surfer uses whatever browser came with their computer. (They don't know or care that others are available.) and they never touch preferences.
You need to understand some will not be the owners of the workstation and thus, even if they could, switching/using/downloading JS, Flash, Silverlight etcetera is out of the question (even more so when they own the damn thing but they have no clue; how do you think they will manage to install Flash, if the browsers doesn't provide a plug-in by default, which many UAs don't). And this, only if their device supports the use of this technology. Also, not all have internet connection plans that will permit them to surf friendly in your bloated web page.

It it certainly NOT a big waste of time, once you manage to see the bigger picture