Both the voltage and temperature could be culprits here - many bulbs are sensitive to overvoltage.
If you are going with LED bulbs, you usually have a wider acceptable voltage range, but you should be able to get the max-voltage info before you buy.
Additionally, LED's have very low heat output, so will be just fine in the enclosures.
So I'd say the problem will be solved by getting LED bulbs (just check that max-voltage on the spec first) - these will last so much longer.
Alternatively, If you are handy with electrics, have a look at the power supply circuit and see if you can reduce the voltage. Are all the bulbs in series? If so, adding a power resistor will drop the voltage (at the expense of some heat generated across the resistor). If the bulbs are in parallel, you'd need to see if there is a voltage control on the power supply itself.
One reason bulbs can burn out quickly is if the voltage applied to them is higher than the expected voltage (120V in The USA). Wiring problems and bad transformers can cause the voltage to be out of spec. Another reason is if there is a loose connection somewhere, and the light flickers (causing unnecessary heating/cooling cycles). A third reason is if the light is in a confined space, and overheats.
In order to check the line voltage, you will need to use a voltmeter. The Kill-A-Watt is a very safe product to use to check the line voltage. Note that you should try a few different outlets, since there are generally two different phases of power (not really phases, but opposite polarities, 180 degrees apart) going into a typical house, and you need to check both of them.
Identifying a bad connection is trickier. Generally, you would see flickering lights, but to be sure you would want to use an oscilloscope or spectrum analyzer (expensive equipment). Sometimes a bad switch will cause a short flicker when the light is turned on. Replacing the light switches with new high quality switches could help.
Finally, have you noticed that the bulbs go out more quickly in certain places? Are those places more confined, causing the bulbs to heat up more? If so, you need to use lower wattage lights (such as CFL, halogen, or less bright incandescents) so that the bulb is less hot.
LED lights, halogens, and CFLs are all more efficient than incandescent lights. For the same amount of light output, they use less electricity, and generate less waste heat (keeping them cooler). In order to check if they meet your needs, compare the light output (in lumens) to that of the bulbs you are currently using. Don't go by the "equivalent" rating (such as 60W equivalent).... The amount of heat generated is nearly proportional to the wattage of the bulb (generally between 10 and 25 W). Another thing to look at is the color temperature, as measured in Kelvins. More orange lights will be around 2700 K, while more blue (daylight) bulbs will be around 5000 K.
PS: Advertised bulb lifetimes are usually assuming use of perhaps four hours per day. So, a seven year bulb may only last a bit over a year if it is left turned on continuously.
Best Answer
I would look for a voltage drop caused by a loose connection in a junction box they tap from or service panel if they all do it, or individually if only certain ones do it. Putting a 100watt lamp in a 40watt socket is a safety(heat)issue (how much heat the fixture is rated to handle), if the fixture cant throw off the heat it would affect the lamps life some, but not that fast.