What they're talking about is the MLC SSDs (older models) had a limit of 10,000 write cycles per "cell" on the drive. With smaller models, you could conceivably wear out cells on the SSD if it was a small SSD, you had a crappy controller and you put the OS on it, primarily because the swap file gets written to continuously, especially if you're stressing the system with something like multiboxing. Newer SLC SSDs have 100,000 write cycle limits per cell, are usually much larger and have better controllers, which mitigates the problem enough that you'll probably end up replacing the PC before the SSD dies.
For more info on SSD technology and the rationale behind the above comments, see
this article.