I understand the argument being made, and it's valid.
Move a single grain of sand on a beach, you set in motion a whole series of subtle changes to the timeline that will have who knows WHAT effect on the future. Those subtle changes will lead to more and more changes that are of increasing significance.
It's possible that someone on the Kelvin was to introduce a Picard to someone they should marry, and because the introduction was never made, the lineage of Captain Picard doesn't happen the way we know.
Could be even more distant. Someone on the Kelvin was supposed to buy something in a shop on their next visit to Earth, and it was the last of its kind in the shop. With them dead, someone else notices the item, takes a few minutes to look it over, and as a result their whole day turns out a little different due to timing, traffic, etc.
What happens to them the rest of that day affects other people around them that they were supposed to interact with in a certain subtle way (bumping into someone while walking down the street, for example). Because they weren't there at that exact moment, they don't have those same interactions, but have new ones with entirely different people. This leads to those people having subtle changes to their day, and to everyone THEY interact with being affected differently in the new timeline...
It builds and builds and builds until Jean Luc is never conceived. Why? Maybe all his ancestors were exactly the same, but on that night...
"Sorry dear. I have a headache."
The incredible odds that on another night the very same DNA pattern would emerge when Picard's mother has hers and her husband's DNA combine inside one of her ova...
It's virtually impossible.
Jean Luc is never born. Instead, two days later, another male child is born, or perhaps a female. Genetically they'd be brother or sister to Captain Picard, but there's one little problem.
They were born in his place and he doesn't exist.
How many times have we heard in scifi time travel stories "Don't change anything or you risk making major changes to the future"?
This is the type of thing that's meant.
Now, imagine all the other changes that could emerge all over Earth, let alone all over the galaxy, due to the "domino effect" resulting from Nero's changing the past.
The ONE chance we have here was already mentioned by someone above. It's a fantastic concept, but since this is science fiction, it's worth mentioning.
What if time itself still carries a roadmap of sorts, and insists on going on the way it did before?
As a result, all the subtle changes more or less play off and absorb each other, and somehow the result is a history very, VERY similar to the one we already know, with certain differences. (For example, Picard needing to visit with Sarek ELSEWHERE rather than on Vulcan in "Unification", since Vulcan doesn't exist any more.)
A number of fans have pointed out that the COUNTDOWN prequel shows Picard and Data intact after Spock and Nero vanish into the black hole and are thrown back in time. This suggests 24th century Trek was left essentially unchanged, or Nero and Spock went back in time but also ended up in an alternate realilty, a parallel universe, and that the alternate reality is where all future Trek stories may take place.
Either way, Picard and Data were still there, so the TNG era is pretty much the same, or exactly the same.
COUNTDOWN proves it, so that end of things is settled.
Now, someone tell me...
Will Uhura still get a run in her stocking during the period the salt vampire visits the Enterprise?
