I feel like people that take these polls vote on trends that Sakurai has had. For example, Mario, Pokemon and FE get new reps for their newest games. We get 1-2 classic retro characters. 2-3 reps from newer titles or series. 2-3 third party reps.
Not aimed at you per se, but these trends tend to be made up by the fans and have little basis in what gets added.
Let's take a look at the Mario series representation:
64: +2 = 2
Melee: +3 = 5
Brawl: +0,-1 = 4
Smash 4: +3 = 7
The series is so capricious it isn't even funny.
Even if we'd look at reps from new games as you suggested, it doesn't stack up. The Melee additions were not from the newest games (well, they were - but not in the way you seem to mean). In Brawl, we could've gotten new characters from Sunshine: Bowser Jr., Shadow Mario or even Toadsworth - but we didn't. Only Rosalina and Luma was
fairly new when they were included: but even they lagged almost
two main series games behind.
Or Pokémon:
64: +2 = 2
Melee: +2 = 4
Brawl: +4,-2 = 6
Smash 4 (projected): 8
Smash 4: +1,-2 = 5 (6 after DLC)
Well, this pattern of +2 netto per game was broken. Granted, Pokémon
does tend to include at least one character from the latest games (though even more from older games).
Or Fire Emblem:
Melee: +2 = 2
Brawl: +1,-1 = 2
Smash 4 (projected): 2
Smash 4: +2 = 4 (6 after DLC)
Again, pattern of 2 total was broken. We only have two points of data between games, yet the entire boards seem certain we'll see a character removed in order to promote a new game - which fits only one of these.
During Smash 4's development, people were certain we'd get a fourth Star Fox rep (Fox in 64, Falco in Melee, Wolf in Brawl, so surely we'd get Krystal in Smash 4) - yet a character was removed from the roster instead.
If there's anything we should be looking at, it's things we
don't really expect: things that break these trends. Wii Fit Trainer, Villager, Duck Hunt, Rosalina & Luma and Mii Fighters (Miis were expected, but three movesets?) are good indications of this in Smash 4. Or Zero Suit Samus, Pokémon Trainer and ROB in Brawl. Or Zelda/Sheik, Ice Climbers, Mr. Game & Watch and even our favorite masochist Pichu in Melee. Many of these aren't considered the WTF character, but
do make you go 'huh, hadn't thought of that'.
Were they expected? No. Does their inclusion make sense? In a way, yes.
The rosters many of us make are - simply put - just too safe, based on these imaginary trends. Rather than listing the characters we feel are from series that would logically make sense to get a new rep, we should approach new characters by looking at what new thing they would do. Characters like the Toy-con Robo and Tibby feel very 'Sakurai' to me, while I feel many of my personal favorites (Dixie, Captain Toad, Waddle Dee) will not make it for this reason: because these guys are usually from familiar series, they just don't have that 'new' groove that Smash newcomers these days seem to need.
I feel like this is also the reason why we saw so much third party characters as DLC - and I'm 'afraid' this will only continue in the Smash 4 character selection process.
(And when it comes to choosing our third party characters, we tend to look at what is popular here rather than looking at Japan. We don't even have threads for Jibanyan and Slime!)
/rant