I agree that most (95%) of the time onheroic 5 man content that the 3 things knaughty said is enough. But 5% of the time its not.
3% = To many casters to round up, too few melee attacks.
2% = Many bosses who do too few melee hits and have more spread out aoe damage then focused on the tank (less SA)
First case think the first few pulls of oculus. Nothing but caster dragons who are almost impossible to round up so you have to drop all your highest cost skills to keep aggro.
Second is fights like oh say magistra from nexus. Spend all my time flying around taking magic damage can pinch my mana.
100% agree this is not for 10 or 25 man content. But for people paying their heoric dues its not hard to switch spec and glyphs as needed.
And although debatable I would say you lose next to nothing for getting it the talents/glyph. The best for raid ret talents seem clear but outside of raiding there is alot of flexability with those ret points.
Every time I try to use a spell and I hear my whiney blood elf say "I don't have enough mana!" I go into nerdrage. Preventing this from happening on my endless heroic grinds out weighs possibly being able to survive the same content with lesser healers. I think that is what the OP is thinking too.
So in the end yes, it is easy content speccing. But doesen't mean you shouldent spec it for easy content

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Limitation strictly defined by motivation - Edan
Warning. I edit my posts.