Psyke, you've got it well enough. I think the only place a font selection will be ignored is in a body selector (perhaps html, as well). The Kobo gives the user the choice of serif or sans-serif at the body level, and the user interface gets complicated when you want to allow or dis-allow a publisher selected font as well. Down in the Workshop forums, there have been great discussions about how much control the user should have over the appearance of ebooks. And I've seen some people who believe the publisher is always right!
By the way, I wonder if the publisher actually obtained the rights to distribute those Ariel fonts... The Tex project does have substitutes, after all.