DivineChaos - they did let someone else be the hero. It was Raiden in MGS2, and everybody cried.
I say that it's indicative of Japan becoming a little less naive about the western video game market. No matter which way you look at it, XBox 360 has "won" this race, with a massive install base and attach rate (the amount of games, on average, that each XBox 360 owner has purchased). It absolutely smashes PS3 out of the park.
Just look at Tekken 6 and FFXIII for evidence. In the past, Namco and Square could be assured that PS2 sales alone would make them profit on the games that they made. Why? Because EVERYONE fucking had one. In Japan, and in the US, and in Europe, and in Australia. It was a largely uncontested battlefield, and yes the original XBox make a slight dent but still the PS2 was just the industry standard for many years.
However, Microsoft pulled some great business moves in buying studios and securing unique exclusive games for their machine, which led to the XBox 360 getting some pulling power. On top of that, they timed it perfectly, allowing the the next generation of games to find their way into the market first, games that wouldn't have worked on the PS2 or XBox (i.e. Oblivion, Dead Rising etc.).
Now you can say "oh, you want MGS4? Well we want Halo" but it certainly doesn't work like that. Microsoft own the IP for Halo, they decide where it does and doesn't go. Even though Bungie could make other games in other genres for other machines now, Halo is Microsoft's baby and the XBox 360's greatest strength.
On the other hand though, MGS is owned wholly by Konami. For the entire previous generation, Sony have beeen quite lucky in the sense that they didn't need to buy loads of studios or franchises because the publishers themselves could easily see that they'll make more money by minimising development costs and publishing solely on the PS2. Sony would make nice deals with them to ensure this happened, and everyone was happy because lots of money was being made.
Except now, all of Sony's buddies are worried because the PS3 install base is a lot smaller than it was projected to be at this stage of it's life. They want to make money, they want to sell lots of games and they can't do that on PS3. They've spent the last three, four years developing these games based on the assumption that there would be a hojillion people with PS3s to play them on. They simply cannot afford to stay loyal to Sony. It would be absolutely ridiculous. Hence, Tekken and Final Fantasy, and potentially now Metal Gear Solid, will have to find their way into gamers' hands some other way- guess which?
So the question we should be asking is - do we want our favourite game developers to continue making money and games? The answer is "I think MSG4 should be ported to XBox 360, thanks."