I don't think so. They would have to prove that the bike was started at temperatures cold enough that the 10w didn't lube as required and as well as the 5w, and that the the 10w didn't lubricate the engine as well as the 5w at operating temps. That would be an awfully long reach for them.
The low number, in this case 5w, only reflects the oils characteristics at cold startup. Other than that. A low number relative to the upper number only indicates a less stable, less able to resist shear and oil degradation than say a 10w-40 or even better, a 15w-40. This is universally true when comparing similar oils. Because it is the modifiers added to the oil that give it the viscosity spread. These additives are not lubricants. And as they break down the oil will change properties.
True synthetic oils, engineered at the molecular level during the refining process, need very little in the way of modifiers. So they tend to be more stable and more able to resist degradation than mineral oils with an additive package.
Once the oil begins to warm, and certainly at operating temperature. A low cold start number is actually a detriment to lubrication and protection. So at operating temps. A 10w-40 will protect better than a 5w-40.
While it is very important to have good lubrication at startup. A true synthetic like Amsoil will flow, lubricate, etc., better than a mineral oil at low temps. Not to mention that a true synthetic stays with metal parts better than a mineral based oil. Which means there is more oil where it needs to be before the engine even starts to turn.
Plus, as I mentioned. Unless your oil temperature has reached sub-zero temps. You don't even need a 0w or 5w oil. I would guess most Spyders don't even see freezing conditions at cold startup. 10w true synthetic oil is good well below freezing.
It is also interesting that no one has chimed in here bewailing the dire issues they have suffered under the scenario we are discussing. Nor have I ever encountered it in real life or any other forum that I visit. I think the reality is that unless you do something really stupid with your oil. It just isn't something the manufacturer can win in court. It's much easier to frighten the customer at the dealership level.