This can lead to conversations like: "You've asked for N weeks vacation but policy is strict everyone starts here with 2 weeks". "I can probably live with that for an extra X k/year." ... "We can do N weeks".
I think in tech 2 week is becoming rare though. More likely either longer, or so-called "unlimited" (which itself is nonsense).
The more weird thing I find in US corporate culture is a tendency to not take the vacation you are allotted. In some countries this is legally at least problematic, in the US it's sometimes a badge of honor.
At most small places where HR is flexible, the PTO package is highly negotiable and I usually leave that to last and tack on an extra week, as they know they want me by that point and it doesn't cost them anything extra.
The conversation does go like you describe at some places, but others are absolutely rigid. One place where I actually accepted an offer, they increased everyone's vacation after my negotiations (small company). That has to be the most goodwill I've had when joining a team of people I didn't know.
But you're right, I never say now. I price it all accordingly, so they can say no.
We also offer an additional 4 weeks (contiguous) once every 5 years, which is not standard for tech and is an enjoyable perq.
* - plus sick time which you aren’t paid out if you’re fortunate enough to not need to use, plus parental leave