As an example, I have no problems in general with backgrounds. +2 to a skill, or an extra class skill, is not a big deal PLUS every character has access to it. Sure, +2 Diplomacy may or may not be more important than +2 Athletics depending on a given campaign, but even then the difference is small. However, allowing your primary ability to determine starting HP is a huge difference compared to a simple +2 to a skill. This can make as much as a 10 point difference in starting HP and makes it easier for a player to min/max as Con is no longer nearly as important (particularly if you already need Str). Granted, every character still has access to this particular background, but it seems clearly superior to others.
I have an issue with people complaining about these backgrounds like they're a bad thing. They aren't really any more powerful, they're options to let you build a viable character.
1. Without them, you make Dwarf/Goliath/etc. even more optimal for melee characters.
2. Without them, far fewer builds for characters are "worth" playing. Assault Swordmage, Brawler Fighter, Tempest Fighter, Thaneborn barbarian, etc. all become much weaker choices compared to their brethren.
3. It makes melee characters rely on more ability mods than non-melee. As some would put it, it makes them M.A.D.
4. It still doesn't make up for fewer surges (which is more HP), it just gives a bit of a HP bump at early levels. Why should non-con melee combatants be the earlier edition wizards of 4E when it means they can't do their job?
5. Classes/builds that use Con still get that nifty background bonus to a skill/whatever non-cons don't get.
They're not that powerful but they give you options. Themes are about the same power-wise but with more flavor attached.
So unless you want a table full of Dwarf/Goliath Fighters/Rageblood Barbarians every time, the backgrounds are a good thing. I'd find that pretty dull myself. Then again there is teh internet "cycle" of new that people come to at different times.
1. New concept introduced.
2. Immediate screams of "it sucks".
3. Some people perceive (often imagined) loopholes to exploit the concept and suddenly the cries change to "it's broken!"
4. They realize it really was not a game-changing monstrosity and move on to the next new item.
We now return you to your regularly scheduled program.