There are some people for whom LFR is too easy and old normal (current heroic) is too hard. The current system fixes this.
I'm going to be running an open guildwide normal raid tomorrow, then our actual raid teams are going to hit heroic mode and potentially mythic. The open guildwide raid is low pressure, I'm setting a gear minimum of 610, I let folks drop out as we go along and I announce in guild chat when we're about to pull each new boss for folks who signed on late, and I'm not going to sweat it if our composition is less than ideal. My old flex raid would often have a heal team of all priests, or 7 warlocks and no hunters, or other odd compositions, but it didn't matter we had fun and killed stuff anyhow. The raid teams are going to ask for commitment to be there and a higher gear minimum, we've planned out who is levelling what so that we have a decent coverage of raid buffs and a nice mix of melee and ranged and clutch utility players.
There is absolutely a need for normal and heroic. YOU don't need the two difficulties, but we welcome them.