One thing you may notice about the templates on this site is that most of them do not use tabs. In fact I make a point of disabling the tab function within the template (which is spelled out in the README file for each template). So if you don’t see the tabs in the photo or on the live previews, you can assume that it will not support the tab function.
The reason for this is that I don’t like the tabs. Back when Amazon used a tabbed menu (which is what the AOM tabs are based upon), I didn’t like them; nothing much has changed since then. I feel they are sloppy-looking and with large category lists tend to detract from the overall look of the site. Many of the templates offered on this site do have a small rollover menu in the header, which works fine if you only have a few categories. Otherwise they’re handy for static pages like About us, Shipping info, Contact us, etc. Or you can take ’em out altogether.
In addition, the rounded menu tabs have always been buggy; there’s no need to retain a site element that may give you fits in certain browsers. As Internet Explorer is dragged kicking and screaming into true compliance with ‘normal’ web standards (as Chrome and FF, etc. already do to a large degree), the problems with tabs may decrease. But from a design point of view, I’m still happier with a nice clean horizontal menu than a tabbed one. It’s about the only part of the standard AOM design that I find disagreeable (other than the Related categories box, but that can at least be relegated to a typical sidebox if you like that sort of thing).
Having said all that, if at some point I come up with a design that allows the use of tabs without interrupting the overall flow, or doesn’t stick out like a sore thumb, I’ll happily leave the option in for the end users to decide. So far that’s only been the case with Atmospherium, where the tabs are changed almost beyond recognition anyway.
And that’s why most of the available themes do not have tabs, in case you were wondering.