And transistor density has nothing to do with performance? Obviously that's not the only purpose of denser chips: you can make smaller chips, etc. But, as David House said, transistor count may actually drive performance faster than predicted by raw transistors. See from
Wikipedia:
The doubling period is often misquoted as 18 months because of a separate prediction by Moore's colleague, Intel executive David House. In 1975, House noted that Moore's revised law of doubling transistor count every 2 years in turn implied that computer chip performance would roughly double every 18 months (with no increase in power consumption).
This was later formalized as
Koomey's Law.