Where I work, security is fairly high on the list of priorities. With that being said, even here things could be more secure. Sure, I have a separate dedicated "admin" login, but I have both full sysadmin to my SQL Server and full local Admin to the same servers. At one time I seem to recall the security guideline documents we use indicated that if an application (such as SQL or OS) could be configured to require logins from two users before granting admin privileges, that that must be enabled.
Arguably, this is a feature that perhaps MS (and other OS and application vendors, as well as developers of in-house applications) should look at making available "natively." On the OS side it could be either an optional component, or something that is controlled by Group / Local Policy settings (and really only two settings, on or off, and once on, it requires the two admin login to turn it back off.) Implementing something like this in SQL Server might be more of a challenge (but it would go a long ways towards stopping applications that "need" SA privileges,) but I'd bet it could be done.
Sure, it'd be a pain when you need to fix something RIGHT NOW and all the other admin-level users are unavailable, or if it happens after hours, but that would be the price you'd have to pay for that level of security.
Such a system would also go a ways towards at least reducing the possibility of a rogue admin wiping out your systems (especially if your logins are not user / password, but user / smartcard & pin)