It doesn't state a PCD antenna size, only states a minimum coupling zone (assuming a credit card sized PICC) for a PICC which is only a little smaller than the size of an Xperia NFC antenna, interestingly enough. Maximum is assumed to be within the size of that same card for obvious reasons.

PCD to PICC connection is basically a transformer, it's two inductance loops with an air gap allowing for transmission of power which is then modulated by one side or the other. The reader modulates output, the tag loads the field for modulation, which the reader can then sense. Two well matched loops will provide more efficient energy transfer and with the proliferation of smaller than credit card sized tags it does not make sense from any point of view to continue making the PCD antenna at near to maximum size.

Where the standard itself becomes relevant is actually in 14443-2/6 which states that the PCD shall produce an energizing RF field which couples to the PICC to transfer power and which shall be modulated for communication.
Frequency error allowable is 13.56MHz +_7kHz, Hmin at 1.5 A/m (rms), Hmax at 7.5 A/m (rms).
"A PCD shall generate a field of at least Hmin and not exceeding Hmax"

So, what happens when your antenna connections get dirty, bent, twisted, impacted and generally fail to make proper contact with your antenna...? Additional resistance will mean that the operating field output is lower than it should be for the power output generated by the PCD. This is because any change in the resistance of the circuit to the antenna not only lowers the current that reaches the antenna but also changes the tuning of the circuit and will result in power going from RF output -> antenna and then partially reflecting back at the output stage due to the mismatch. The device will no longer comply as Hmin should be read after the antenna.

In my opinion, and it is only an opinion and obviously not a reality, manufacturers of quality equipment should use proper RF connectors and links which ensure that this does not happen. A device which is in proper working order and complies with the standards will read the NFC ring. A device which does not cannot be said to comply - it is no longer functioning correctly. This is less of an issue when the antenna is smaller, more closely matched as the energy transfer is more efficient and the field more dense - though it would be very interesting to take readings from a number of devices and see what they're actually doing in terms of output strength.