Optional Installs the Mandatory Standard?

Isn't it strange that both Microsoft and Sony don't have any rules when it comes to installations of game data on the hard drive? And isn't it even stanger that all games don't let you play the game with and without installations on the PS3, just like the Xbox 360? Why is it mandatory in some games on the PS3 to install usually GB's of data?

I can understand if for multiplayer the data isn't installed, then everyones game will load differently and require synching, but there's no excuse for the single player part of the game. I'm on the 40GB HDD PS3 and it's definately not much space to work with, I know that 80GB is the standard now, but even that can get filled up quick when many games install more than 4GB onto the HDD. Add in downloadables from the PSN store, some, like the ones you buy which take up permanent space on your hard drive and it will fill up quick. Bought a new game with a mandatory install and your hard drive not have enough space? Tough, you'll have to delete something to play it. Then wait while it installs and finally get to play the game. It reminds me back to the old days when I used to play PC games and the waiting for the new game to install...

So what if it takes longer to load? Let me install the game data if/when I want to. Then there's the opposite end of the spectrum, being unable to install any data to make the experience more enjoyable. Let's take Killzone 2 for example, what the hell is up with that? There's no manual install option and what's the result? When playing the single player game, the checkpoints often stutter and the game needs to load the next section off the disc. If installing data on the hard drive would have made it a seamless experience (which I'm sure it would!), then why wasn't the option there? I think this is even worse than a mandatory install. At least let us have the option, if we want faster install times.