Whats The Difference?!?

You forgot to mention the idea of other cool items, like BOTD or Breath of the Dying...Such an awesome weapon .And. About this end of season how does that work out? Do you start over in ladder or are you moved to non-ladder and what happens to your items? Do they get deleted?

I don't believe that ladder monsters are harder than the non-ladder monsters. I think all monsters (in both Ladder and Non) got a revamp in the 1.10 patch. Also, the ladder seems harder because everyone hard to start from scratch without the uber items they had become used to.
FYI - the cool items like BOTD are available in Non ladder games. There are a few exceptions but not all that many.

sickfic04 is right this is taken directly from the arreat summit.

Ladder Games Have Increased Difficulty
Ladder Games offer a more challenging type of gameplay than players will find in Normal Games. Monster AI speeds have been increased. Reaction times increased for Ladder Nightmare and Hell games. Basically every monster acts like a super unique. Monster Hit Points have been increased for Nightmare and Hell Ladder games too.

No one still has told me about the reset...your scaring me about the word RESET meaning redo or start over

Basically in about a year (when a new game should be out considering lod is 3 years old and d2 is 5 years old ) they should come with a new idea and not take 5 years to make it and make a new game. So stop whinning and if not a new game you just stay with your current chars or move to ladder just like now, duh.

When a ladder season is over (We haven't finished one yet, so they're fairly long.), all ladder characters are moved to non-ladder with everyone else. They keep all their stuff. Then, players will proceed to make new characters in the new ladder.

You do not have to make new characters. You can stick with your old characters, but you will not be able to get ladder-only items or advance with the majority of the players who move to ladder. (I expect the ladder community to be 20-40% smaller than it is now, which is still a large amount.)