Do I really need to go into this again?
Did you ever read comics as a kid? As in READ them just to READ them and experience the stories, follow your favorite characters, etc.?
Well I did, and before sportscard dealers brought this whole "rookie card" mentality to comics in the late-80's, people actually READ these things, so ask yourself this:
If you are looking to READ and collect a back issue (remember, there were no TPBs) about your fave character's past exploits, would you choose:
a) a comic with the first single panel of your fave character and no cover appearance.
or
b) a comic with the first entire story about your fave character and an action cover image.
That's why "first FULL appearances/covers" were more popular and worth more historically pre-CGC, and will continue to be, as in the CGC entombed comic world, covers mean more than ever.
You don't need to shoehorn a first appearance label onto a particular issue just because it is the more sought after book among a character's early appearances. You add more legitimacy to the book by separating it from being associated with a character's first appearance, as it is then allowed to stand on its own. You don't need to call 181 the first appearance of Wolverine to sell it as a desirable issue, the cover and it being his first fight with hulk are enough.
Ask yourself this, how many comic book stories end with a teaser, hook or whatever on the last page to get you to want to buy the next issue? When that teaser involves a new character, the hobby has always used "cameo appearance" to describe insignificant first appearances by characters.
So some people argue that the technical first appearance is the only appearance that should warrant a label that claims to be "first".
No one is shoehorning a "first appearance" onto a label, the people arguing for cameos as legitimate "firsts" are trying to rewrite history for whatever reason. This all pre-dates CGC labeling and the hobby's use of "cameo" to describe a first 'minor' appearance comes hand-in-hand with our almost universal understanding that first appearance generally means first "full or feature" appearance.
This is what everything boils down to. It's that some people are taking the "first" in the term first appearance way too literally. Like they've stumbled upon this great hidden secret that the word "first" has been misinterpreted by everyone in the hobby for many decades.
Heck, some are even claiming that Previews, the solicitation magazine, should be fair grounds for first appearance recognition.