He's talking about architecture rather any any pros/cons for Arm vs. x86.
Most (all?) x86 PCs are the same - they have a CPU, they have a BIOS, the BIOS boots such way, they have the same interrupt controller, they have a chipset that allows you to self indentify cards and the like.
ARMs are put in a lot more diverse hardware. Some may map their firmware at xyv, some at zyx. Some ill have an interrupt controller, some might not - ARMs are put in hardware where saving $2/device can give you big $$$$$ savings over 1M devices.
I guess if someone got together and put together an ARM hardware spec, mandating you have this firmware, interrupt controller, system device than ARM as a workstation/server platform would evolve, allowing the software to make assumptions about the platform itll run on.