:: racking memory ::
OK, got it. Mental transposition arising out of discussion of shoddy Font Substitution in MSIE 8 for Linux. Not everything Microsoft is Windows. Oops.
I know DejaVu only as a full-spectrum Unicode font (it's third-party for me too), which is why I wondered if it's necessary. If the user doesn't have DejaVu they're bound to have some other sans-serif font that can do the job for a much smaller investment than 600K.
And, oops, I've been assuming DejaVu Sans because that's the one with the biggest character range. DejaVu Serif is not much smaller-- and just as interchangeable.