The reason for the hypothetical question is that Apple have a poor desktop line up. At the consumer end you have the mini or an all in one. Neither has decent graphics. At the 'Professional' end you have a product that is too expensive for consumers - it's aimed at the professional market. I want an Apple desktop, but there isn't currently a product I would buy.
You consider the line-up poor because you want graphics power. Not everybody cares about graphics power, and so for those people there is a mid-range desktop...the iMac.
A point I'm trying to make here is different people have different needs and requirements. I personally would call the iMac high-end because all I see is the price on a computer I'm not interested in. If I personally need price-effective performance then I have my PC. If I want to use a laptop I adore using then I have my MBP. If I want a simple, quiet, low power computer which I also adore then I have my Mac mini (always loved the idea of the mini ever since it was announced). You get the idea.