You make some good points, but it really comes down to is speed vs. cost.
"The iPhone can already get up to 100kbps on the average over EDGE and has promised to deliver us HDSPA (Mbit range).."
BTW, this has nothing to do with the Pre. They just want to support existing customers, so they don't go to Verizon or AT&T. And want new customers to pay more by having them buy cellular modem.
It's all greed.
Sprint allows the these phones to tether:
Blackberry 8703e, Blackberry 8130, Blackberry 8330, Blackberry 8830, 1HTC Touch, 1HTC Mogul (6800), 1HTC Apache (6700), LG Fusic LX-500, LG Muziq, Motorola KRZR, Motorola RAZR V3c, Motorola, RAZR2, Motorola Q, Motorola Q9c, Palm Centro, Palm 700w, Palm 755p, Samsung A900, Samsung A900M. Samsung A920, Samsung ACE, Samsung i830, Samsung SPH-m520,Sanyo SCP-8400. Sanyo Katana, Sanyo Katana 2, Sanyo M
The Pre is nothing special, and Sprint has no idea what it is doning.