It certainly states that handloads should not be loaded to +P, but since some handloaders use fresh brass, where's the difference.
In the manual it states that handloads and remanufactured ammo are not to be used due to poor or nonexistant quality control. It says nothing about new vs. old brass.
It also infers that the approved pressure for the gun is standard SAAMI and not +P.
It infers nothing of the kind, nowhere is SAAMI mentioned. It says
"If you prepare your own handloads be very careful, and do not exceed recommended pressures in line with those generated by standard factory loads (not +P) as manufactured by Remington, Winchester, Federal, Hornady, PMC or other reputable companies." All of the above manufacture NATO spec ammo for the military and European markets. They are specifically stating do not HANDLOAD to +P specs.
Read the actual paragraph from the manual, its talking about handloads specifically.
Go here and read this as well
http://www.waltherusa.net/p99.htm
"Available calibers include 9mm (a.k.a. 9mm NATO, 9mm Luger, 9mm Parabellum and 9x19)"
Note the 9mm NATO, which is considerably hotter than SAAMI.
Buy a Walther P99 with confidence, it is a superbly engineered and manufactured weapon. Which will hold up to any amount of shooting that you can put through it in a lifetime.