Why standard voltage is $110/220~\mathrm{V}$ and not $500~\mathrm{V}$? Why do we have standard voltage $110/220~\mathrm{V}$? 
I mean electricity delivery savings (or wastage when heating the to thin cable) by switching to higher voltage would be enormous more power delivered using same lines. I am sure that some smart people have considered it before, is it because of safety or there is something else at play? 
 A: Safety is the reason why it is done so. Higher (than $110\mathrm{V}/220\mathrm{V}$) potential difference between a human body and a circuit will result in a very, very severe electrical shock. Of course, power loss can be quite minimised by increasing the voltage, but that will be at the cost of lives of all living species that either accidentally or on purpose come in contact with such an electrical circuit.
A: Well, to be fair 415V is the standard three phase line voltage within the UK.
Each house is connected (generally) to a single phase, hence 240V 
Vphase = Vline / SQRT(3)
If you want Vphase to be 500V - Vline would need to be increased to 500.sqrt(3) or 866V !
The domestic supply in the UK to your house is unbalanced - there is live and neutral.  This means that the live is 240V with respect to neutral - neutral is supposed to be within 10V of earth ground.
Theoretically (and I am not suggesting you try this) you will not get a shock from touching the neutral line.  This is why isolation transformers are used on building sites or damp conditions.  The supply is now 'balanced' equally about earth and lowered to 110V.  This means that there is no live and neutral - each AC line is 55V with respect to earth but 110V to the other line - the shock you would receive by touching a single line (you provide the path to ground) is reduced to a much safer level.
As with all thing engineering, there is a compromise between cost, safety and efficiency.  Be thankful however that Edison didn't get his way, or we'd have been stuck with DC as our domestic supply! http://www.smithsonianmag.com/history/edison-vs-westinghouse-a-shocking-rivalry-102146036/?no-ist
A: Distributing power at low voltage would indeed be uneconomical. Everyone knows this, and it is common to transmit AC power over high tension lines at 200 - 300 kV, in order to minimize joule heating in the several miles of conductor running to your house. This voltage is transformed to 240V very close to your house, so there are no large transmission losses because the transmission distance for low voltage AC current is small. The OP's implication that significant power would be saved by running house current at high voltage is not true, as the VERY small electrical savings from doing so is just not worth the much higher personnel risk from doing so.
A: It's both for safety and for practical considerations. Above 15-50A connectors and switches and circuit breakers get heavy and expensive and the danger of fire due to overheating increases. Above 120-300V safety is considerably less (especially if there might be water present) and either the users have to live with the lack of safety or thick redundant insulation, interlocks and such like has to be used. At even higher voltages there are issues with arcing (and corona discharge, which produces ozone which is a nuisance and tends to degrade some dielectrics). 
When the standards were established, a typical home would use very little power by modern standards- perhaps less than 10kW. So 120/240 seemed like a reasonable compromise. Some big houses today have one or even two 300A service panels, so as much as 144kW of power capability. 
If technological changes (perhaps powerful electric cars or in-house energy storage battery banks) results in homes drawing or supplying power levels significantly higher than is currently used, then higher voltages might become attractive, as would 3-phase power. After the aluminum wiring fiasco, we're stuck with copper and the cost of copper wire goes up proportionally with the current for the same loss and length.
Industrial power in Canada often uses 600VAC 3-phase and in the US 480VAC 3-phase is common. 
A 3-phase 15kW load with 600VAC (line to line) requires less than 15A per conductor, which is quite reasonable. The lights in the particular office I'm sitting in now use 347VAC switches and ballasts which is line-to-neutral on 600VAC. The electrical bits are better made than the typical cheap home 120VAC ones, but not radically larger- the wall switches are similar toggle types to those in a house, with a bit more pronounced 'click'. 
Changing a widely adopted standard is very, very expensive and most likely we'll soldier on with what we have for a very long time, but there's no reason why we couldn't have had 480VAC or 600VAC 3-phase power in houses. It would have been a bit more expensive to distribute because an extra conductor would be needed on all streets and all pole pig transformers would have to be 3-phase, but would have resulted in more use of efficient 3-phase motors and significantly longer service life of electronics. 
