Pinch-zoom not pure zoom in Web browser on HTC Desire Z because text is auto-re-formatted: irritating / layouts break
I believe this feature is called text reflow and is not an actual a feature of Android but more of HTC. The HTC browser reflows the text as you zoom in. This can get very annoying especially because after reflowing it can move your focus area to the closesr text not what you were zooming into.

My personal pick for an alternative browser is Dolphin Browser™ Mini. It has both the functionality you're missing in the stock HTC browser but also the speed you expect when loading webpages and launching the browser.

Dolphin Browser™ Mini