New Postal Charges: shapes and pricing

Have you seen the upcoming changes for postage from the USPS? Not only are stamps going up (as my friend M said–no one has managed to use up their 2 cent stamps from last time yet) but now they are changing to “shape” based pricing.

They sent out an email at work about it–reminding people not use interoffice style envelopes for mailing etc etc.

Why is the post office making life more difficult? I’m never going to be able to remember what shape goes with what…