Except that's not really true. Trademark dilution has nothing to do with parts of speech, per se, much less plurals. Xerox's ad campaign to try to get people to stop using their trademark as a verb tried to prevent genericization, but not because a verb is somehow bad. They did it because people were using Xerox as a verb to mean copying something with a copy machine, regardless of who made the copier. Bayer didn't lose their trademark on aspirin because people used their trademark as a noun. They lost their trademark because people called products by other companies aspirin. And so on.
This is why you won't see Google, for example, complaining about people using their name as a verb. Now if people start using it to mean "Searching on Bing", they might, but that's not the same thing. A trademark becomes genericized when it loses its meaning as a brand identity—that is, when people start associating products by other companies with that term. Up until then, you're fine.
With that said, the iPad brand name actually might be in some danger of becoming generic. It's scary how many people ask for help with their iPads, and it turns out that they need help with some Samsung device or something. This is a danger that any company must face if it is the first to popularize a new category of products.
In an ideal world, Apple should never have used their trademarks as nouns, but rather should have consistently called them "iPad tablets". If, in all of their literature, they had consistently used "iPad" as an adjective, there would be much less risk of genericization, because people would naturally have picked up the word "tablet" and associated that generic noun with that class of device, rather than "iPad". Unfortunately, it would also have meant that fewer people would have used the word "iPad", which would have weakened the brand's impact on the market, so it's a two-edged sword.
Either way, though, the problem isn't that the trademark is being used as a noun, but rather that because it is used as a noun, many people misuse it to describe products that aren't actually iPads, naïvely thinking that all tablets are iPads. Moreover, any attempt to prevent that by telling people to say "iPad devices" just makes that problem worse, because the word "device" is too general for people to latch onto it. Apple should instead be telling people to say "iPad tablets". That way, people will get it through their thick skulls that an iPad is a particular type of tablet, and that the generic name for that product category is "tablet".
