From an article by the EFF:
> The circumstances under which a company could actually lose a trademark—such as abandonment and genericide—are quite limited. Genericide […] is very rare […]. Courts also set a very high bar to show abandonment (usually years of total non-use). Importantly, failure to enforce a mark against every potential infringer does not show abandonment.
[1] https://www.eff.org/deeplinks/2013/11/trademark-law-does-not...
Call it a myth if you will, blame it on overzealous lawyer who just want to create work for themselves.
My only point is that this "myth" is so powerful that it creates a business reality where these suits are ubiquitous, but it's only news if a company like Apple does it.
At most you can make an argument that estoppel can apply. Estoppel prevents you suing somebody for doing a thing you agreed they can do, even if you would have been allowed to sue them for doing it if you hadn't agreed they could do it. But estoppel doesn't magically extend to other parties.
I'm not going to an enter into an armchair-lawyer contest with you. My understanding of the law is indeed limited, but it reflects what is going on in actual business.
Another possible explanation is that their lawyers are having a quiet period and either want more income or want to demonstrate their value. Oftentimes there can be an internal logic to these things that on the whole makes little sense but within an organization is perfectly rational.
There really shouldn't be a case here. The logo is different, the trading area is different, there is exactly zero chance of confusing the two designs or the two companies.
It's like when you have a team of lawyers with the job of looking at contracts and licences, they will start suggesting changes even if that makes no sense because they're paid to suggest changes. See jslint and the special "can be used for evil" licence.