You are competely right BUT - try going into Jaycar and asking the clerk for a "One N 4001" and see what strange stare you get. If you said "I would like an IN4001" he will have a better chance of knowing what you mean (maybe).
In all products I design and build I always designate this part as "IN400X"
I agree that you are correct however....
Original will probably be IN4001 or IN4004 but IN4007
Just to be a pedantic twit, because I can, the diode designation is actually 1N400x.
The 1 signifies the number of junctions in the semiconductor device, one for a diode. Transistors, which have two junctions, when following this naming scheme are 2Ns.
That said, I'll get of the soap box and crawl back into my hole 
