I've noticed plenty of little nuances just off the numbers..
if we've had an uptrend the prior day, R1 and R2 are usually smaller in range and the S1 and S2 are wider apart. Therefore, it is much easier for price to trade up and it will take a ton for price to head down to the S1 and S2 level. Likewise, the reverse is true for shorts.
Also, some people consider that the market in an uptrend would never be weak enough to trade down below the S1 level even in retracement days unless there was true weakness and may signal a reversal.
Other logic behind pivot numbers are floor traders like to bounce around between R1 and S1 and any move outside of this range indicate a swing trading force that pushes the market out of balance into a trend.
After a large trend day, the calculated distance between the pivot levels can often be relatively large with price chopping along on low volume and maybe just touching one pivot level the whole day. Traders who base their strategy off these numbers will have no trades all day since they are never reached... thus perhaps contributing to the chop. The reverse is also true for narrow ranges, where the following day may reach 4 or 5 different pivot numbers .. increasing trading activity and perhaps a trend... ala NR7 and WR7 type days.
Surely, this is no coincidence and someone must have formulated the numbers off of something.