It is much different. A hard drive can be written in the same spot over and over again without much worry.
In consumer level nand memery chip(MLC), each cell holds 2 bits(or 3 for some strange stuff that should be in ssds some time in the future). Now each of those cells can only be program/erased(you erase it then place the data on it) so many times. For older flash it was something like 8-10k times. Now the newer stuff is 3-5k in most cases. As you have seem from the link, it seems you can push well past those numbers.
Back on topic, if you lets say update a file every day(think of all the logs your computer edits on a daily basis) and it writes to the same spot in the nand, it would fail rather quick(worse part is that you would not wear out the drive, just that section).
To make this issue worse, the cell has to write BOTH(Or THREE with that stuff that is still not used yet) of those bits at the same time. So if you have to add another bit to the cell because it is only half full, the drive has to erase then write the 2 parts at the same time. You can imagine that you would wear out the drive real quick this way. By the drive keeping all the flash wearing at the same time, your text file has to write over the drive time and time again allow a much greater life span for the drive it self.
USB flash drives do the same thing.
This having to have to write the full cell every time is also why if a SSD firmware does not do its job right, you get slow downs. If a SSD has tons of half filled cells and no more free cells, it has to wait while it prepares clean cells(erase) for writing. This is when the performance takes a hit. TRIM as well as background garbage collection allows the drive to try to get those clean cells ready before they are needed to give you better performance.
To make matters more interesting, consumer level flash comes in more then one type.
Async - Cheap, but good enough for many users.(cheap, but gets the job done.)
Sync - Better and used in many SSDs(Medium Price)
Toggle - Considered to be the BEST you can get.(expensive, but performs better in many cases.)
This is a good article on 60gig Sandforce(Controller) based drives, but has stats for some non Sandforce drives as well. You will also see that sometimes benchmarks to do not effect the real world performance.
http://www.tomshardware.com/reviews/ssd-60gb-benchmark-review,3137.html
With higher end commercial or server level drives a different kind of flash is used(SLC).With this expensive memory, each cell only needs to hold 1 bit. This way, you never have to free cells and performance is better. Another side effect is not extra PE cycles are wasted to clean cells because you NEVER have to take off data and rewrite to add a second bit to a cell. This stuff cost more, but has great performance.
May be worth a look at this as well
http://en.wikipedia.org/wiki/Multi-level_cell
EDIT
And...
Sorry for taking this WAY off topic.
1000's and 1000's of gigs written and erased from SSD's to make me feel better about nand life 
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