You're being downvoted because, simply put, you're wrong.
One gigabyte is as large as any other gigabyte, yes, but the characteristics of that gigabyte may be very different. If they're predictable in some manner, you can tailor a compression algorithm to that gigabyte.
You can learn some about this by studying linear algebra.
And information theory. The salient concept here is the "entropy" of a chunk of data. The maximum degree to which a given sequence of numbers (or symbols, bits, etc) can be losslessly compressed is called Kolmogorov complexity. Wiki away! :)
