Well, that's totally true but then it comes to a point where you have to decide if the next "jump" is good enough. For example, Broadwell is almost the same as Haswell, but Skylake will improve in various areas with new features. So if someone has an Ivy bridge there's no point on not waiting for Skylake and going Broadwell now (unless their computer dies). That's why i bought a Haswell with the lowest config (4gb ram, i5...) to resist one more year till I go to a 15" Skylake.
It won't be really noticeable compared to last gen, for now, but when the time is passing by, you realize there are big differences between some generations of hardware. For example, my MBP 2010 still was a C2D with Sata II. I thought it was OK to buy it just a month before the early 2011 gen, but the time shown that 2011 gen olds much better than 2010 for stuff like: thunderbolt, Sata III (I could only reach 240MB/s with a SSD on Sata II), i5/i7... It's not like "yeah, its 1 year younger technology so it will be better" but "it brings much more benefits, despite the time that has passed".