Pockets are for mouth guards...and I think just to carry on tradition, really! Also I doubt the ref's whistles sound different...maybe it's just how they use them, louder bursts coz more players or coz some players wear head gear...totally guessing here!

Don't know about the whistle but the pockets are used to out your mouthguards in and in the younger ages it is used to help lift in line outs but thats just in Australia could be the same elsewhere like NZ but you never know

Depends on the refs preference and the whistle used. The WRU recommend the Acme Thunderer for their referees, FIFA endorse the Fox40 Sonik, a pealess whistle with a very distinctive tone. I use a Fox40 Caul, a pealess whistle with a finger grip.

some second rowers prefer to grab a pocket instead of a shirt. my whistle does not sound different.

I belive the pockets are for your gum shield if you wanna take it out and also could be used to bind as well i belive the tone of the whistle is because it carrys better in rucks mauls and scrums plus in the lower leauges most teams share a ground with a football team so you can tell the difference i may be wrong but its the best i can think of

rugby refs have mics over which the tv audience can hear what they are saying. maybe they need a different type of whistle to be heard over this. just a guess