The X-men movie timeline has been altered by the events in this movie...how?

Rating: 8/10 (1 June 2014)

I really enjoyed this movie, but even though I'm not a huge x-men fan (I haven't even seen all the movies), it's obvious that the timeline of the movies has been changed by what takes place in this one! If you consider Mystique's capture after she originally kills Trask, following which she is experimented on to perfect the sentinel robots, this quite obviously means that she is no longer alive at the time of the original X-men films (assuming her brain is dissected, as is certainly implied when Trask discusses her biology later in the film). Magneto being imprisoned in 1963 also implies that his history will differ from that already seen to date. Wolverine's rescue by Mystique at the end of the movie implies he won't be acquiring his steel claws as originally shown either. And to cap it all off...Professor X is alive in 2023! Forgive me for the number of spoilers, but they lead up to my point...how come the writers and directors have introduced time travel into the X-men movies only to create an alternate timeline to the previous films, unless they've done it deliberately?