Very true, I would also prefer something that works even in a text based browser. I've never really 100% fit in with the user standard, being one of the first to browse the web from my mobile phone (Nokia 6230i back then) or using alternative browsers when MSIE's market share was still >90%. I've had more than enough compatibility trouble to go along with something working on only some systems.
(For example I'm currently building a website which will also support everything from high-end desktops to text-based terminals. Only disqus comments are a pain, making the page size go from 23KB to over 500KB and requiring Javascript, but the tradeoff seems worth it--trust me, I thought it trough over and over and over lol.)
I don't know that search engines use tab order to parse fields, but they very well might and could.
I know that especially when it comes to web-based admin tools, something that:
1: Works well with keyboard navigation.
2: Works (at all) in a console-mode browser.
... is going to get a hell of a lot more interest from me than something which:
1: Doesn't readily support keyboard nav.
2: Doesn't work in a console-mode browser.
3: Requires Flash.
4: Requires some specific/minimum browser version/release.
5: Requires MSIE.
From 3 onwards, these are instant death for any enterprise tool I'm evaluating.