I think the main problem is that you're looking at these articles with the mindset that these suits are being carried out over a superficial or surface level similarity, which--while not unheard of (see, for example, the recent trademark trolling of Take-Two Interactive forcing Hazelight Studios to abandon their trademark for the game
It Takes Two)--would be a frivolous and legally questionable dispute. Not to mention, a waste of everyone's time. But the links you've provided (at least those that I can see) are much more grey than that.
The Hershey one is full of broken links, so I can't really see that one, but that is a trademark dispute, not a copyright dispute, which is not the same thing. Trademark is a symbol associated with a property, rather than the property itself. The golden arches on the McDonald's logo are the obvious example. The big, red M. on Mario's hat, the leaf in the Animal Crossing logo, the typeface used in the Disney font. Anything that connects a work visually with its brand. Again, many of the links on that article are broken, so I can't say whether or not they'd have a case, but it's not just a matter of something being similar. It's whether or not that something is similar enough to cause confusion. The orange packaging of Reese's candies are iconic to their brand and if Mars was using a similar color, intentionally or otherwise, in such a way that it would lead consumers to confuse their property for Hershey's, then that it is a case of infringement. It's essentially how bootleg and knock-off merchandise operate. They use similar or identical typefaces or other artistic elements to confuse laypersons into buying something they believe is from the official company when it is in fact not.
The one with Prince and a few of the ones in the last article are disputed on the grounds of rather the pieces are
transformative enough to be considered fair use, which has been a grey area of the law for a long time. Most of these are not just artistic pieces inspired by other pieces, but
edited versions of copyrighted images. One of them (the Freddie Mercury/David Bowie suit against Vanilla Ice) even straight up uses samples from the original recordings, which is a bit different from how Croc might bare some resemblance to Yoshi.
So these cases aren't about two people creating art that happens to have similar properties, though there have been a number of suits which have been predicated on that. Wikipedia has a
long, though not exhaustive, list of songs that have been subject to these kinds of cases. Regardless of their legal merit, it is questionable how many of these actually
should have legal ground, from a moral standpoint. But that is the unfortunate landscape of copyright law: There is no formula that determines whether or not something is infringing; it's based largely on human judgment, which can often be flawed or swayed by external pressures.
As for the last question, if you are found to be infringing, a company may submit a DMCA/cease and desist notice, warning you to stop before legal action becomes necessary. But as far as I'm aware, this is more of a courtesy than a requirement.