This particular piece of advice requires more space for the rationale than the others :

13.   On CW – do not slow down to match a     caller’s speed.

If someone calls you at a slower speed in your pile-up, it should not be necessary to slow down to match their calling speed.

Is this 'inconsiderate' operating?   No

Is this 'arrogant' operating?   No

Is this 'impolite' operating?   No

Would you expect a top DXpedition CW operator - for example Stan LZ1GC, working a big pile-up of stations at 40wpm as T2GC, to slow down because you call at 25wpm?     No

Firstly, the station calling you in your pile up should have checked your callsign (if they clicked on a spot they should still have checked that the spotted callsign was correct) and may have been listening for a minute or two so will know the next serial number, etc.

Secondly, in contests where the exchange is predictable (no serial number) most calling stations can recognise their own callsign at a higher speed than they normally would use for sending.

You should adjust your sending speed if propagation conditions are unsuitable for higher CW speeds.

Obviously, if you are calling a slower station, then it is usually sensible to match their speed.