They usually don't announce the big stuff until E3 actually happens. These are just smaller announcements to create a buzz before the start of the show.

Maybe there is going to be even bigger stuff at E3.

Every year around the middle of Spring you start to see a dramatic upswing in game announcements. This happens just about every year. This is a good time of year for mid tier games to make an appearance, gain some recognition, and draw attention to their holiday arrival. Without the risk of being overwhelmed by the larger games showcased at major events.

The reason it is pronounced this year is that its also coinciding with the minor blush that precedes the conference. Which is usually due in large part to developers getting what amounts to cold feet. They usually planned to unveil at the conference, but after getting the lay of the land they decide it is better to stand out in the cold.

So it is both a combination of standard operating procedure, and the chaotic nature of every developer working with their own agenda. Then you obviously have the intentional leaks that are used to drum up interest, or are the result of failures in security. So this year you should see a greater then expected bump. Do not let the moment blind you to the pattern.

Wasn't it the same last year?

Well, some smaller publishers, like NIS which just announced 4 new games, use this time to get info out rather than get lost in the wave.

well so far the big 3 hasn't announced anything "big" so hey who knows ^^

I am still hoping for pilotwings and Kid Icarus.

M$ has been pretty mum on the details, so...

It's usualy Sony/MS/Nintendo that have the big "surprise" E3 annoucements. Third party multiplatforms get announced early, while big exclusive announcements get announced at E3 press conferences.