Yep, I've known that the '10,000 steps' isn't an magical or meaningful number... but an arbitrary number picked almost at random.
I think it works though, as 10,000 steps is more than what the 'average sedentary person' would usually do, plus '10,000' is a nice round number to aim for.
To be fair, anything that helps motivate more people to be a little more active is a good thing... so if a person averages 3000 steps and manages to increase that average to 4000 steps, then that is still a positive step (pun intended!)
I used to obsess over getting 10,000 each day (to the point where I'd be marching on the spot in my front room before going to bed). Thankfully these days i don't take it as seriously. I average 20k on 'busy days' so if I only do 4000 steps on a sunday*, then thats ok :-)
*unless I notice I'm at 9,600 steps, then I will walk circles in my front room to hit 10k, its all about that number bias!