ORIGINAL: Jeremy Z
I'm sure it is because that is the assembly that n00bs screw up the most, with disastrous consequences, and Tamiya probably found it cheaper to remove that element of chance than to try to help these folks get it right.
Tamiya's manuals are really accurate and easy to understand though I suppose the odd person stuffs it up and for people who want to run it as soon as possible it decreases the build time.
Aluminium parts.....Will that be blue aluminium Lee?