I don't know how 10k became the rallying number for walking. Overall steps help, yes. But what's important is the amount of walking you do outside your own daily activity. I.e., if you walk for work- this doesn't really count (unless you're a mail delivery person, perhaps).

Time spent is probably more important than actual number of steps, in my opinion. A one-hour+ walk (in addition to your normal activity, divided up across the day), regardless of how fast you go, is more valuable than a walk that nets you 5,000+ steps. Not everyone can walk 5,000+ steps in a day, and not everyone should try to reach that.