While admitably I discovered this only after making uncoverable changes to the DF raw data files, I think that the fact that there be things going on where you'd think things ought not be going on was worth the submission.
So I was reading up on various item and material values and the relationships between them on the wiki, and after topping that off with a look at the magma-safe materials page I decided I was going to add some extra tags to metagloss_metals to open up the possabilities - one of those "why not?" sort of things. Nothing major, just making stuff like Platinum and Nickel/Nickel Silver and Electrum forgeable into anvils and armor and stuff for the pricier metals, and when I finished I went and generated a new world to see how things had turned out.
When I selected my standard loadout, though, I got some nasty messages - "you cannot afford this, you cannot afford that" - and it was all stuff I'd used multiple times before without a problem. After doing some detective work, restarting the PC and rolling back to vanilla raw data (admitably I've got several files I've tweaked), I finally traced it down to metagloss_metals, specifically the (ANVIL) tags I'd put on some of the entries. Wierd thing, though? Only nickel/nickel silver caused that point interference - not platinum, not electrum, not the numerous entries I'd added to them for other things. And it wasn't even just changing them, either - in tests I did the (ANY_USE) token didn't do a thing for either metals in terms of embark points.
Long story short, there's something at work regarding the nickel/nickel silver entries that makes DF flips its lid that bit more and start hacking away embark points whenever you make 'em anvil capable - from the 2060 available points I've goten in vanilla tests it goes down to 1260 for nickel and 1360 for nickel silver - and I figured that between Toady's reported shifting of more things to raw datafiles from hardcoded stuff and people doing their own modding and tinkering it was worth bringing this out.
EDIT: So DF determines your embarking points after calculating the value of the default load-out instead of using a set value from which the default values are subtracted? Interesting, if not a bit puzzling/convoluted - time to snoop around and see if there's any reasoning behind this.