Iwata was most likely thinking about costs associated with the consoles and games developed for them. The specs themselves doesn't matter if there's no development resources (i.e money) to utilise them.

But not only do the operating systems hog large chunks of system resources, visible differences also require multiple times the processing power.

Firstly, multiplatform games weren't that popular at the time. All the consoles focused on exclusives. But the Gamecube missed out on plenty of multiplats. Grand Theft Auto being the largest one. 

Its pretty straightforward. Poor sales didnt stop big games like Soul Calibur and SSX from being on the system. Tell me how many games were on the PS2 and XBox but not the GameCube?

Is there a list of such games.

There where a ton of games Gamecube did not get. It got only the first two Burnout for example. Blood Omen was ported, the later Legacy of Kain wasn't. Other games like Tomb Raider Legends came about half a year later.
Don't have a list auf multiplats that didn't make it to Gamecube, but you could compare total release lists and pick the games that where Xbox/PS2 but not GC. And then there's games lake TR Legends that came out much later.

Gamecube already had a mediocre to poor support.

Wii U could in theory have gotten all those multiplats to late 2013 and each and every cross gen title. And all that stuff it never got, except a few games. That wasn't about GPU-power or RAM.

The real next gen games, well, that's another story. But it's not like we have so many of them yet.

There are about 12 billion reasons why third-party developers and publishers avoid the Wii U. Each one of them might not mean much alone but when added together they become more compelling.

You're comparing RAM from a console to a PC. Completely different.

Nintendo didn't had quality control with third parties. There is plenty of massively broken NES titles that they just put their seal of approaval on like LGN movie tie-ins. They even made the Power Glove! What they did was to block any title that they believed that would compete with a first party offer. They affected directly the profit of 3rd parties because they manufactured all the cartridges and Nintendo would determine how many copies would be made, not the 3rd party (who actually made the game). Best part? Nintendo manufactured X cartridges and sent you the bill. If they tought your niche title neede 1M copies, better pay for it.

N64 limiting the devs for their own good? Cartridges were more expensive to manufacture, they were making the lose money. The only thing N64 did was block them to do the pre-rendered cutscenes the public wanted.

Nintendo politics just had one objective: guarantee that Nintendo 1st party games had a unfair advantage and guarantee that Nintendo controlled everything around 3rd party games. So, when the first guy promissed something better (Sony), 3rd parties jumped ship praying for better days.

its so Axed on 7 gen colsoles that it seems attacked by a really angry Freddy Krugger. Same with a lot of other games. Its just not the same experience. 

you are making a shallow specs comparison. and it's not like the games should run the same.