No they're not. 2.5" refers to the platter diameter. There's no specification that requires them to be a fixed length, width, and height.
Most are the same width and length, but not all are the same height, which is why previous large drives (with three platters) did not fit in the MacBook Pro.
The WD one is two platters and should be short enough to fit in the MBP.
There are people who haven't had problems installing them in a MacBook Pro.
Also, the dimensions of it are the same as there 120 GB model.
My MBP has a Fujitsu HDD, and the dimensions are the same for the 320 GB WD HDD.