If you "suffer through" an unusually long streak (high wait time for blocks, dice rolls under 7, etc), then at some point you have to get fast blocks or high dice rolls in order for the stats to normalize. Is it accurate to say the dice have long-term memory? 
Not according to the laws of math (i.e. a random number generator could produce a number < X for years without being flawed).
Again the "difficulty adjustment" is used to "try and fix" this sort of problem (in terms of adjusting based upon the history).