All PSPs can use the web browser. You just need to update the firmware to do it (V2.0 and above) and this can be done to any PSP regardless of it's age or supplied firmware. You seem to be under the impression you are stuck with the features that come on the PSP when you purchase it. This isn't the case providing you are willing to update it. There are, of course, advantages to not updating your PSP - it just depends on what you view as being important. Easy homebrew on 1.5 and below or additional features on 2.0 and above, the web browser being just one of them.
Personally, I view easy homebrew as being infinitely more important than the web browser which I would never use anyway. Even though limited homebrew is now available on all PSP's (see threads
http://www.psp-forum.com/viewtopic.php?t=5453 &
http://www.psp-forum.com/viewtopic.php?t=5401 for details), it still can't compare to the ease of use and 100% compatibility that homebrew on a 1.5 PSP provides which is why I have no intention of updating mine just for features I will rarely use.