Hi ducksmack,
It’s certainly not true that “all new beds feel great”.
While nothing has a 100% success rate … with a local purchase and for the majority of people … careful testing using the guidelines in the tutorial (rather than just testing for the more subjective “comfort” of a mattress which often won’t predict how well you will sleep on a mattress or how it will “feel” when you sleep on it at home) along with some good guidance from a knowledgeable and experienced retailer or manufacturer that has your best interests in mind will usually result in a mattress choice that is well inside a suitable comfort/support range and will generally be “close enough” so that if any fine tuning is necessary it would be relatively minor and involve different mattress pads, sheets, mattress protectors, or perhaps even a topper if a mattress is too firm (see post #4 here and post #10 here).
No this isn’t true although most hotel mattresses don’t use particularly good quality materials. You can read more about hotel mattresses in general in post #3 here and the posts it links to.
Phoenix