Digisparks aren't programmed via avrdude, and the bootloader doesn't support eeprom read or write - this is part of how the digispark manages to have a 2kb usb bootloader, where the previous smallest was about 2.8kb.
There is no USB bootloader for attiny85 with avrdude compatibility because the tiny85 chip cannot be compatible with USB if it needs to do flash erasing or writing as the chip freezes up for several milliseconds during those operations, crashing the USB connection. This is why the digispark uses a dedicated upload tool "micronucleus" which carefully manages the usb traffic of the host computer to keep it from doing any queries to the device while it's dead, so the computer doesn't realise there's anything wrong. During the 'connecting' stage the bootloader communicates to the host how much time it would like the host to wait after each write or erase operation before resuming USB traffic. It still bugs out and crashes half way through sometimes, but we are getting better at avoiding that and also automatically recovering from those errors in future versions. Leet hax!
Aside from the USB crashing issue, the reason USBaspLoader cannot be 2kb on tiny85 chips but it can on mega328 is that the tiny85 doesn't have hardware bootloader support, so there are more leet hax in there to implement one purely in software which takes up extra memory.
