You are looking at it from one point of view remember.
What you say it true, the apps that have been written do run fine, however, yes, they will run fine as the fixed point in hardware was in place so apps had to be written to run well on this.
In the same way as devs write for games consoles. The hardware is set in stone and you write to this and nothing else.
You don't write a program for the PS3, the Wii or the 360 which needs a machine with twice the power to run your code well. That's just not the way things work.
In the same way, if the iPad was twice as fast as it is now, and apps were written for that, and then you took those apps and ran them on the iPad we actually have, then they would run bad as they were designed to run on a different system's power.
There is nothing WRONG with the iPad now, as you say, all things that have been designed for it run good, well yes, they would do
The issue is going to be, what will devs do when they do have more power to use. Will they use it?
Well a game released later in the year need 512MB or ram to run, or need a dual core CPU to run with a smooth frame rate? (the iPad 2 we hope)
There are many heavyweight apps that can't really run on the iPad as it is for various reasons. And of course games can always do with more power, memory etc.
In 5 years time, we will probably look back at our current iPad and be amazed anything worked with such limited power and memory etc.