> Yes, a seat is a seat, but once you're
> locked in into a vendor, you are locked in.
If it's easy for other car manufacturers at much bigger scales why would it be an issue for Tesla?
On the outside, it is a seat. What is different between manufacturers, and even between cars: dimensions of the components, abilities of the seat (e.g. how many degrees of movement, heating, massage functions), the attachment of the seat to the car itself, the form of the seat... if you want to switch the seat vendor, you have to account for weeks if not months until the new vendor delivers the same final product.
> If it's easy for other car manufacturers at much bigger scales why would it be an issue for Tesla?
They don't switch or only switch at model "refreshments", which is at odds with Teslas always-improving workflow.
If they have professional supply chain and commercial departments they'll have contingencies in place for situations like this.
Even companies as massive as VW can not handle such a situation (as evidenced last year: https://www.ft.com/content/ffd3ee62-6934-11e6-a0b1-d87a9fea0...).
... and thus very vulnerable to strikes or arbitrary price hikes. Yes, a seat is a seat, but once you're locked in into a vendor, you are locked in.
Tesla wants to avoid lock-ins as far as possible and especially something where a switch to a different manufacturer is as difficult as a seat. You can switch a vendor for a simple plastic part in a matter of days if the need arises (and the 3D data for the forming process is your IP), or do multi-vendor sourcing from the start - but try switching your seat vendor, that ain't gonna be cheap nor in a reasonably fast time frame.