I don't think you're aware just how much GW1 changed from the beta weekends to release date.
UI/Skill acquirement/tons of skills/etc changed completely, to name a few.
No obviously I am not aware! But aren't those the same thing as just 'polishing' up the game? Instead of creating new things? Skills are a given because those are always being changed/added.
Generally alpha is when a game is playable, it's when all of the things that the developers wanted are added. Beta is where the game starts to get polished and balanced, as well as tested by a wider selection of people to see if they like the game, it's also very possible that during beta they will completely redo/add/remove skills, stats, features, UI, basically anything based on the feedback they get. The following games are all in beta and they've all had many very large changes done over the duration of their beta; Tribes: Ascend, Dota2, and Natural Selection 2 (I'm sure there's others but these three I have witnessed the changes first hand).
That's just ideally though, many companies use the term "beta" as "demo", where the beta is basically completely finished and there is almost nothing the company is willing to change completely.
Isn't that exactly what I just said?
Edited:
Also that second part was a quote for GWguru forums