My take is that nobody is doing better than Pi in terms of the community Pi targets, e.g. students, amateurs and greenhorns alongside professionals. There's a critical mass with Pi that attracts industry players to be on the platform with what counts for decent support in the embedded world, e.g. Microsoft and Canonical.
Always. Everywhere. Wanted 25 units to teach a robot class to some local kids at the Hackerspace. Had to buy 3's instead. Even if I'd placed 25 separate orders, the cost of individual shipping on each vs the cost savings of the combined shipping on the 3's put the price within spitting distance.
Pi zero is an ad. A loss leader. A way to have an answer, any answer, to the flood of $7 Allwinner wonder-boards on AliExpress.
The Zero is a very different devboard, though - you will need to invest in assorted adapters and hubs if you want to connect it to just about anything other than power... it is useful in small spaces, but for anything else spending a little more to get something like the CHIP is well worth it, and for use a small PC, going to the RPi 3 is probably wiser.
The Raspberry Pi 3 is available from many vendors for $35 + sales taxes. You can pick it up on our site for £32 including VAT (that's EUR30 before taxes or EUR36 including taxes): https://shop.pimoroni.com/products/raspberry-pi-3
For me, that's worth $15 per board.