4.1 is some major changes and some new dungeons.
This is filler content, yes, for the top end guilds who want to raise alts, or those mediocre guilds catching up- it gives more time.
We're not losing a raid tier, it's just delayed a little - They want to give us an amazing raid instance.
I would personally like to see Raids on the scale of MC/BWL/Naxx - with plenty of bosses to sink one's teeth into. If they're delivering a raid instance on that scale, then no one will be complaining that it's delayed a little.
Unless you're Paragon/Premonition/One of those guilds, there's PLENTY for you to do still. If you can't find something to do, cancel subscription til the new raid tier comes out? Seems logical.
I think some of the people in this thread are over reacting.