While the argument can be made for using the ultrasound every time, I think everyone needs to gain the ability to put them in blind. There are events in which time is of the essence and waiting for an ultrasound can put a major drag on your ability to care for a patient in the way you'd like to.
Just the other day, we had a patient code in the ICU due to hyperkalemia. Attending asked for an art line. I ran to get the ultrasound for my co-resident and when I got back to the room 30-40 seconds later, he had already threaded the catheter and was attaching the pressure tubing. Delaying that art line another couple minutes maybe wouldn't be life or death, but this allowed us to get an ABG a couple minutes faster and further correct her K+ (which was 7.0).
I've seen other cases as well in the OR that merited a rapidly placed arterial line (trocar through the IVC in a cholecystectomy), and being dependent on an ultrasound would have delayed care.
I guess I'm not arguing against the ultrasound so much as I'm arguing in favor of learning both skills.