Warranty can not be denied because the brand of oil or filter used. Look up the Magnuson Moss warranty act. If your dealer tells you that you must use OEM oil and or filters for warranty requirements then they are required by law to provide then for free. It is important to use oil and filters that meet the manufacturer requirements but the brand is not important. With all that said sticking with the OEM oil and filter does take all the guess work out of it.
Yup, fully agree, and you kinda made my point about the warranty. If by some bizarre chance you do have an oil related failure, being able to show that you've been using the factory oil and filters- and this goes for any brand machine- you will avoid all the inevitable questions that will follow if you use a brand other than O.E.M. I work on Honda outboards, and over the past 10 years, I've only had three engines fail that could be blamed- one for sure- on an oil related failure. The very first words out of the Honda rep's mouth were... "what kind of filter were they using?" and then- "do you have a record of the oil changes, and brand of oil?" No warranty was denied, but in one instance where an aftermarket filter was used, it took weeks, instead of hours to get warranty approved. I don't doubt for one second that there are better oils, but I can tell you from years of experience and conversations with the Honda rep, and tech people, they are absolutely adamant that Honda oil is the best oil for their engines, and I couldn't get any one of them to even waver, or hesitate on that question, and believe me, I tried.
So I tell you guys what I tell my customers- Just use Honda's oil and filters till it's out of warranty, and then use whatever you want.