If the plane crashes into the ground at 500 kts, that's that. No change if it's a Piper Cub or an A380, apart from bodycount. But if you are a passenger, you do not much care if you die alone or not.
However, from the viewpoint of survivable emergencies, the 747 was considered safer that the contemporary competition since it incorporated many extra safety features (for example the third wing spar). Larger may well mean safer since there are (normally) more safety features in the form of more redundancy.
All accidents are different and it is hard to really come up with a correlation between size and safety. For sure, if an A380 came apart in flight, the body count would be higher than if an EMB-135 did, but it would be misusing statistics to conclude that the A380 is thus, by it's very size, less safe. This is why for example http://www.airsafe.com
calculates statistics based on the proportion of passengers who died, not based on the absolute number. If 30 passengers die in an EMB-135 accident and 70 in an A380 accident (assuming that the accidents are comparable, and that's a big assumption), it can be argued that the A380 is safer because a larger proportion survived. So size does not matter in this case.
Certification requirements are the same for all planes carrying 35 (I think it's 35) or more passengers. So they should all be considered as safe imo.
If nothing else, would you rather go through severe turbulence in an A380 or an EMB-135? Think about which one has more inertia. Thought so.
If an A380 and an EMB-135 landed in very severe crosswind, which would be more stable? Thought so.
If an A380 and an EMB-135 experienced severe wake turbulence, which would be more likely to flip over? Thought so.
NOTE: I am not bashing the EMB-135. It's simply conveniently small for my comparison.
EDIT: Economic reasons limiting size will always be more important. These can mainly be divided into two categories:
1. Limiting size of airport facilities in the form of runways/taxiways/gates and so on.
2. Limited market as size increases, while production costs keep going up.
[Edited 2004-02-29 17:42:20]
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