Crashman already gave a pretty good explaination but I'll give you my explaination from a programmer's background.
Whenever I want to make a program, I have quite a few options. I can get at the lowest level possible and tell the cpu each and every stupid instruction i want it to do or I can group those instructions to create another set of more complex instructions which do more per an instruction, but cuts down the number of instructions i have to issue by quite a bit.
This is how technology works, it lives on what was done previously to do more. So the actual result isn't instantly complex, it was fairly complex before, and was given a little bit of additional functionality to improve it.
The simplest way to explain why it 'expands' so fast is to take a look at how the computer stores data.
It has already been explained that data for a computer is stored as 1's and 0's, on and off, hot and cold, yes and no, true and false... any two values. So if that one 'switch' as we'll call it can store two values, then by having just one switch, we have a total of two values (stupid, but had to be said). So let's say someone else came along and gave us another switch, so we have 2 switches storing two values per a switch. Now we can store a total of 4 values by combining the two switches. There wasn't any additional 'big' advancement, i mean, we just added another switch and our number of possible values doubled! As it turns out, each additional switch doubles the previous amount...so the mathematical way of determining the amount of possible values is 2^n where n is the number of switches.
What does this have to do with technology? Well, by taking a look at the example above, we didn't reinvent the new combination of switches, we just tacked on a new idea to an existing idea (we had a switch, then we thought about the possibilities of combining switches). This is exactly what we do with technology, someone doesn't re-invent everything about a cell phone over again, they take what was already invented and add a new factor to the bunch to make the number of possibilities expand.
Now you're probably thinking, it still doesn't make sense, someone comes up with one simple thing and it makes our technology double--shouldn't the new idea expand technology in a linear sort of manner? The answer is no: let's take a look at our switches again. Say we had 8 switches, that 256 possible values. Someone comes along, adds another switch, now we have 512...and another 1024...2048, 4096... etc. The end result is that the graph is NOT linear, it is exponential, a curve.
This means that while someone does add in a new simple idea to the bunch, the simple idea will probably be applied to many different areas of the number of existing ideas. So say we as a total had 10 total ideas (club, pole, whatever). Then someone comes along and finds out about the usefulness of sharp objects. Well, if applied 'sharpness' to our club, that makes it something like a sword and if applied to our pole, makes it something like an axe or spear. So you see, the same idea though simple was re-applied to the pool of ideas to make it seem like it did a lot, but it really didn't.
<b>Does it work?</b>
Yes!
<b>Ok, How <i>well</i> does it work?</b>
Uhh...
Yummy 
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