Tell an enterprise you want Amazon to host their software then spend a few days/weeks/months explaining that Amazon does more than just selling stuff. HP is well known, and trusted. For your average start-up, no, there's no difference. But for the enterprise having a name you know is very important. It's why people will pay so much for Oracle software over open source with support contracts.
Most enterprise tools vendors are positioning for AWS support/compatibility as well. I'm attending a BMC webinar in a few minutes that's squarely focused on AWS.
The point about brand names is more about loyalty, in my experience. Companies that buy Oracle will continue to buy Oracle. Companies that buy HP are more likely to pursue an HP Cloud offering. It's all about established relationships and sales channels.