It would make more sense to tie this rule of thumb to a measurable index (i.e. the Russell 2k or a Technology ETF) rather than just pick an arbitrary number. Both are down about 50% from a year ago.
I agree that times have changed, but this seems a little too far, even if it is just a rule of thumb.
Also, there's a tendency for these types of rules to become self-fulfilling prophecies.