ResMed costs more online. I don't know whether it costs more for brick and mortar DMEs. It may just be that ResMed is more serious about price control for online sales.
I suspect the "one brand" prejudice is mostly just ignorance. They often have had a few problems with "Brand X" in the past and remember that. Every time after that, even if Brand X has no more problems than normal, every problem or drawback of Brand X reinforces their previous conclusion. Then they get used to Brand Y, learn about it, develop an emotional attachment, etc.
Or their "Brand Y" distributor is a better salesman, better distributor, or looks sexier than the other distributors. Brand Y may be better at stocking equipment, shipping,
sales support, repairs, financing, billing, training, etc.
All retailers try to reduce the number of brands they have to deal with, train on, and stock parts. It's easier to stick with just Brand Y and try to steer all customers to that brand. Unless they're going to lose business, they'll only stock one brand. Yet another reason we need more competition in the DME business.
Not all of these reasons are nefarious, but realize that what's good for the DME isn't what's good for the customer. Brand X may be a pain for the dealer, but Brand Y machines may work much better for the patient.
In my opinion, ResMed and Philips Respironics are roughly equal in terms of quality on their top line machines. It's most important to be sure to get a fully data capable machine.
Get the free SleepyHead software here
for information on the main alternative to CPAP.
If it's midnight and a DME tells you it's dark outside, go and check it yourself.