Interesting observation, and in fact, the Era 300 looks identical as well.  So I looked into it to see if the dimensions are the same.  They only specify height for the stand for Era 100 and 300, so that’s only thing you can really look at.

Sonos One - 32.98 inches

Era 100 - 35.8 inches

Era 300 - 37.64 inches

So they are not the same.  But maybe that height includes the height of the speaker?  Maybe speaker height explains the differences?

Sonos One - 6.36 in

Era 100 - 7.18 in

Era 300 - 6.3 in

Doesn’t look like it. I would guess the heights are different so that the woofer/tweeters are each at what’s considered ideal height.  It would have been nice if there was a standard stand and pole universal to all, with a smaller extension piece for the various height requirements.  And agreed that Sonos makes more money by having you buy all new stands, but the savings to customer to upgrade only part of the stand would only apply to those who happen to have a pair of Sonos Ones already, happen to have the existing Sonos stands, and won’t be repurposing those stands along with the Sonos Ones when the upgrade.  Even if you sell your Sonos Ones, you could probably add $75 or so to the sale price when you throw in the stands and make up whatever it’s costing you to buy full stands rather than just the pieces you need.

I spent way too much time thinking about this.