While i agree 130$ is way too much money for this little gem, neither a teensy nor a raspberry pi can do everything that this can. Combined they can, almost.
There are other reasons but the main ones are:
Raspberry Pi: no USB device connections, only host (No built in way to connect pi as a usb device to pc) (so a pi serves an entirely different purpose)
Teensy: Only the teensy 3 supports usb emulation with all endpoints going both in an out, no ethernet support without a shield, cant run an operating system, and perhaps most importantly... no security features compared to the armory.
The armory is kind of a bastard child of the teensy 3.1 + raspi or beagleboard but its the same size (near enough) as the teensy.. I'd buy one if they got the price down to like 70-80 bucks.