I had to replace a gas tank on my '96 Blazer, Rusty. It had holes from rust. I have another Blazer with a shot engine that I am using for parts to get Rusty running and inspected. While replacing the tank, I noticed the fuel input pipe had a hole in it as well. Both Blazers are the same year. Fortunately, the one I'm using for parts had been sprayed underneath with rust protectant. Look at the difference in the pipes.

Was the protection done by the original owner as a thoughtful precaution or is it an option for a new vehicle? Is this done on new vehicles now and, if not, why not?

From the looks of things underneath, Rusty was used off-road quite a bit and the other Blazer never. Go figure.

 

Undercoating is always an option when buying new. However, from the looks of the pipes I'd say one was driven regularly during the winter with plenty of salt on the road and the other wasn't.

 

AJB is correct but I have also found that some years of these filler necks were more susseptible than others: My old 96 driven from day one in northern New England still had a nice solid filler neck when I retired it 2 years ago at 256K due to body rust.The 97 I replaced it with has always been a mid-atlantic car and with 184K still has no bubbling or perforation on the body, but the spring shackles and filler neck were TOAST!

 

What happened to the shackles? Mine are pretty rusty but it didn't look like they wouldn't hold up.