There is a patch there, it just didn't get reviewed in time for Firefox 4.
Also, the Firefox team is implementing that but it didn't make it into this release. You can find out all sorts of things they are working on at http://wiki.mozilla.org.
Also, Chrome has had that feature for over a year and in that time it's won a lot of praise from a lot of places. Granted, it's just one little feature that doesn't matter that much... but that's what people refer to when they speak of "polish" and "user experience" and I think that stuff matters more to people than you might think.
Btw, the relevant option in about:config is "browser.tabs.closeButtons"
Values... 0 - One close button only on the active tab. 1 - Each tabs has its own close button (default) 2 - Removes all close buttons (no close button, right click to select option to close the tab). 3 - Display a single close button at the end of the tab strip bar.
ctrl+tab to cycle through tabs