1. WHY TUBE? (A)
The main trouble [from my point of view, of couse] in games - it's background animation. Especially it's critical for action games, yeah? When you make a race - you wish whole the world skimming over you. But world - is a terrible thing - it has so many different objects.... And your brain waits for alot of details - and if you don't give him his common ration - he understands it very quickly. So - your game will be as realistic - as more details you will force to fly past you.

One of logical ways [IMHO] - put several pictures at background of your game - speed will depends from width/height of the pictures, but won't depend from picture's content - you can paint anything you wish - as detailed as you need - and it won't affect on your game speed. But we are in the Web - and as many pictures you put into your movie as high it's size will be - and as less serfers will see it. That's why - we need something ciclic - to limit number of required background pictures[size of the movie] - and nevertheless make the motion endless. That's why - tube. It's ideal - from this point of view.

2. WHY BLUR?
Think you've noticed that the tube and the objects are blured. [if it isn't so - I'm happy - you just played and didn't concentrate on trifles :) ]. There are at lest reasons to make so.
2.1. It's a hint for your brain - "hey, see - it's a fast motion!" :) if you see a blured object your brain automatically tries to calc "visual speed" for the object - speed with that it could move - to be so blured. So blur - it's a simple trick to inclease speed of your game for free :)
2.2. you can set quality of blured JPGs to extremly small values - 10-20 and anybody won't notice it - it's concerned with JPG pack algorithm - you just help to the technology to work. So - it's a good way to decrease size of images.
Oh yes... you can make this blur in photoshop - Filter->Blur->Radial Blur->Zoom, set amount to 20,f.e. click Ok. Wow :)

3. WHY TUBE? (B)
Other important moment - it's collisions. If you use images in your game - you should be ready that they will be rectangles - in this situation still possible to use hitTest - but at this case you should use rectangle-like objects... if you draw a circle and will use hitTest - your clients will kill you sometime - 'cos they will collide with air - empty fields around the circle.
So - would be great to invent other algorithm. Everything is simple - for a tube - you know it's rotation, you know rotation of an objectc inside a tube - and can define range of angles - if your tube has _rotation between A and B - for an object C - your hero is collided with the object.... As u see - it's simple to make for 2d games - just you will compare X of the hero...

There are the most ideas that u can find in this game. All the others - it's just AS code - nothing special or hard - and it has no sence to concentrate on it. It's too simple.