That's the problem though I think and in large part one of the reasons that Leopard got such a bad rap.The iBook G4 2005 models (A1133) that came with Tiger had a default amount of 512 MB RAM. Granted, it was upgradable to 1.5 GB but I don't know if the option was available with the order.
It's true that Leopard needs more ram. But the current mentality of upgrading to the max whenever possible is something that has only recently taken hold on the average user. Most Mac users of that time period were just plain comfortable with whatever they had and expected everything to work as they upgraded the OS.
If you upgraded the OS and got a speed hit because you didn't upgrade your ram then who or what do you blame?
Let's face it. Most Apple users (with few exceptions) are completely intractable when it comes to upgrading. Oh, the anguish and knashing of teeth when Apple introduces something new that requires a hardware upgrade! Even us!
If it were up to us we'd all still be using PowerPC chips running, what? 10.5.9?
So, there's my point. Tiger users of the time just expected to be able to use their Macs in whatever way they had them configured with a brand new pretty OS. But, it just didn't happen that way.