I suppose it has to do with commerce.
When you work in a company with offices around the world, the emerging markets in Europe, the Middle East and Africa (including Russia/CIS) are often grouped together under one division, while the Asia-Pacific region is separate.
I was just talking about this with my other half and she thought it was perhaps because the Middle East is often seen as its own thing: even though it's no more a separate continent than, say, Scandinavia, sometimes it can seem somewhat disconnected, especially for those people who tend to associate Asia with its eastern bits--that was something that took me a while to get used to, that in the US, "Asian" would generally mean someone or something from Japan, China etc, whereas here in Britain it's more synonymous with India and Pakistan, the more far eastern bit described as, well, the Far East!
The commerce bit also makes sense, though it's a bit of a curious one since it seems to encompass a bunch of disparate markets to my layman's view, and wasn't a term I'd heard until the mid-to-late '90s.
Edit: darn typos.