To backup the power control issue here are some technical docs that explain UMTS power control in more depth:

Power Control in UMTS « Mobile & Wireless
UMTS Power Control

From the first one:

"From the point of any cellular network, proper power control helps in keeping interference at a manageable level while improving capacity and the overall service to the mobile subscriber."

And

"UMTS, unlike GSM, has a greater need to combat the near-far problem. A UE close to the Node-B transmitting at the same power as another at the cell edge, will potentially block out the latter."