Wet cleaning every other shoot is not routine maintenance. Every time you wet clean you risk damaging your LP filter. Although fairly hard these things are not unscratchable, and they are very thin and thus not unbreakable. . A misplaced piece of debris, a little too much pressure and mistakes are made.
Additionally, proper wet cleaning supplies (note: pec pads web site state they are not guaranteed to be used for sensor cleaning and have not been tested for this purpose) are not cheap.
Very occasional wet cleaning, or wet cleans after shooting in very extreme conditions are routine maintenance, and certainly if you are confident in your wet clean skills the odds an occasional clean can cause permanent harm is very low, but still present.
If Nikon screws it up they are responsible to replace it, if you screw it up you are on your own. If one is not confident they should get it done professionally.
People are screaming bloody murder because a camera that needs to be manually cleaned that often with normal use is obviously defective and it costs over $2000. I understand that logic. Not every copy is like this, in fact quite a few people have copies that have no dust or lubricant after 1000s of shots. This confirms the bad ones are not normal but defective.
No other DSLR on the market has had this many reported instances of this issue, it is not normal. It is certainly odd that this impacts the d600 so much more than other Nikon's made in the same factory, but such it is. Nikon has been their usually vague self about this issue, admitting it exists, but providing no details on cause or what they have done to correct it for the future. That also has some people ticked. These are all people who desperately want to shoot the d600, one of the world's best DSLRs. It is frustration as much as anything else.
This problem should not be overstated, but neither should those who have it be made to feel like they are some sort of whiney jerk.