Usually I'm not very talkative when rules-wielding is the topic, but this time, I'm a proponent of calling the official rules as they are terrible and completely nonsense. When I read about this specific topic, it seems to me that the responsible for the core rule book had just forgot that the term vehicle means a little bit more than a car or a plane.
I understand how Sichr is argumentative on the "going by the book" way (that couldn't be made more clear than you did on the game where I first introduced Gentleman John as a character), but here the GM in me is being quite annoyed. Hell, I guy receiving armor for standing in a bike make no sense at all (and if we take in account the way Sent just described the dodge maneuver of the guy, it would make even less sense to consider vehicle armor to him). And even though rules are an abstraction, one of the things I like about Shadowrun is that it's not so simplistic as D&D and the like.
When we were playing the War in Heaven, Sent introduced a House rule regarding astral visibility that was not cannon, but fluff-wise made sense. Part of the GM work, besides narrating interesting stories, is to improvise the ways of making these stories possible and more entertaining to all - at least to a part of me, that means, among other things, sharpening some rough edges of the rules, in a way that they can make more sense. As always, I guess that's Sent's call, but in a debate about "official core rules" against "simple yet realistic rules", I am all for what makes sense.