This thought came to mind, reading your success story.
There are some OS parts that do or don't get loaded during a clean install of W7 based on the BIOS settings at time of install.
For example, if SATA Emulation in BIOS is set to IDE instead of the Intel/HP strongly recommended setting of RAID + AHCI then critical drivers don't get installed and you'll crash on boot. Thereafter with this situation if you change BIOS to boot with SATA emulation set to RAID + AHCI (preferred) or AHCI alone you'll get a blue screen crash. This was essentially unfixable in XP, and MS had a FixIt that used to work for W7. Then they stopped their FixIt idea.
I'm wondering if BIOS is set to Hyperthreading-disabled before a clean install that will also result in a similar issue. Perhaps some critical driver does not get installed and then when you later try to enable that in BIOS you end up with an OS crash.
The HP OS install image that comes from the factory would have a master level install that the HP engineers have fine tuned. You don't get the same with a clean install off the MS install DVD unless you know all the tricks.....