Processor confusion

While doing research for a new Notebook, I came across what can only described as processor (or CPU) confusion. I know about some of the differences between Intel and AMD Processors for Desktops, but this was confusion caused by Intel-only Processors:

Mobile Intel Celeron
Mobile Intel Pentium 4-M (or Mobile P4)
Intel Pentium M
Intel Celeron M

The Intel Celeron and Intel Celeron M confused me because of vastly different clockspeeds. A notebook with a 2.6GHz Intel Celeron chip costs about the same as one with a 1.4GHz Intel Celeron M chip while they have similar specifications (like Memory and Hard disk size) Only when I read this article on PCMag.com did it sort of make sense, with the performance of a 1.4 GHz Pentium M being roughly similar to a Mobile Intel Pentium 4 running at 2.4 GHz.

So I assume the same must apply for Intel Celeron M and Intel Celeron processors...