Yes you are correct that you can do a start up just by filing for an S-Corp in Deleware online and then file with your local state.
The catch is that when HP does the 0% they usually run a D&B on your corp and then do a credit check with your corp's bank.
The 0% is an excellent way to attract businesses in to upgrading their technology. As a rule of thumb, you have to upgrade every 3 - 4 years or so, but companies have been stretching it out. With a 0% option, it will drive customers to continue on the 3 year cycle.
3 years because Moore's law works in the SMB's favor so that even if their server needs don't grow, they can afford to downsize, reducing the maintenance costs on their software licenses along with using less energy and have a quieter machine room. (If they have a machine room).
Its a smart thing to do.
Unfortunately the AC is right that 0% isn't for everyone. You still need to have excellent credit rating and show a consistent cash flow for several years.