They are one and the same, 'character optimization' is just the term that clever self rightious players use to describe it when they do it.
So, let's just cut through the pretense and call it all min/maxing.
That said, min/maxing is a perfectly natural thing for all players with any experience and brains to try to do. It even happens in the animal kingdom. From an evolutionary point of view, all animals evolve traits that allow them to gain the most benefit from their environment by expending the least amount of energy. They are min/maxing!
When people go shopping, smart shoppers are looking to gain the most benefit by spending the least amount of money. They are min/maxing!
IN REAL LIFE, EVERYONE TRIES TO MIN/MAX EVERYTHING IF THEY ARE SMART!
So why is it so odd or so bad when it is done in a fantasy setting?
When a player makes a character, they are trying to make the most effective character they can by spending the least amount (or a limited amount) of points. That is also min/maxing, and the act of doing that is not a bad thing in and of itself. I expect players to try and min/max their characters.
Min/maxing takes a turn for the worse when there are game breaking flaws in the game mechanic that allow the player to completely over power everything in their path. It is kind of like 'magic:the gathering', you know that card game. Every now and then there is this killer combo that someone plays that just totally owns everyone at the table.
Expect your players to min/max, because they will. The more intelligent and creative in the bunch will hide their min/maxing behind things like character optimization, or sayings like "it fits with how my character should be roleplayed". blah blah blah, they are just better BS'ers than the rest of your players, but they are still min/maxing little ho' bags. Actually, they are often the worse offenders.
Here is the solution the the problem. As GM, you should take an active role in making the character. Players don't make their characters, the player and the GM make the character together. Nip game breaking combos in the bud from the very start. If a particular trait is obviously too powerful, JUST SAY NO! If a game breaking combo is discovered during game play, then change it/ban it/modify it, etc. Reward the player who found the flaw in the game mechanic for being clever. Often times, problems with min/maxing arise because of a flaw in the game mechanic.
As GM, you should have a clear vision of what kind of campaign you want to run, and the power level. When players pick abilities that are beyond the scope of that power level, it is the GM's job to regulate those things.
As GM, don't be shy about taking command of such things. Players will whine from time to time, but let them. As GM, you also act as therapist/babysitter for the players, so you have to learn to deal with these things. The care and feeding of players is a fine art after all. The players will accept your rulings so long as you strive to make their experience more fun and you are fair.
That is my opinion on the whole min/maxing thing.