Power - your wifi router puts out about 0.1 - 1.0 W, your microwave oven puts out 1000W.
It would take a lot of wifi routers to cook a turkey - more than you think because the antennea on the router is designed to spread the power evenly around the room rather than concentrate it on the center of the oven.
There is a danger of being 'cooked' from being close to very high power transmitters such as some warship's radar while they are operating.
ps. It's the same reason your laser pointer can't be used to cut steel plates (or James Bond) in half!
For most sources of radiation, there are two factors that diminish the power with distance. The first of these is the inverse square law, which tells us that every time we double the distance to the source, the power per unit area drops by a factor of 4. This makes sense from the perspective of conservation of energy - the sum (integral) of energy over all directions must be constant.
But there is a second factor that becomes more important at large distances, and that is absorption. While the inverse square law assumes no losses along the path of the radiation, that is not the case in the real world. Attenuation follows an exponential law, and at sufficiently large distances from the source, attenuation will dominate the calculation and lead to an exponential drop off of source intensity with distance.
For the case of WiFi signals, the attenuation in air is small (but the attenuation in walls etc. is substantial). The equation you quote is for the dB power level ignoring attenuation. If I have
$$P \propto \frac{1}{r^2}$$
then on a dB scale,
$$\log(p/p_0) = -2 \log(r/r_0) $$
Where $p_0$ and $r_0$ are the reference power at reference distance.
Note that is NOT a $\frac{1}{\log(r)}$ relationship ... that makes no sense at all (and is demonstrably wrong, even for a dB scale).
UPDATE:
Reading this answer again a few years later, I now see that it's possible that the equation the OP was shown (and possibly misremembered) included
$$\log{P} \propto P_{dB} \propto \log{\frac{1}{r}}$$
Power in decibels does indeed scale with the log of the inverse of distance (but not the inverse of the log of the distance...). Note that whether it's distance or distance squared just changes the constant of proportionality in log space...
Best Answer
The wifi router, as well as cell phones and microwave ovens all produce non ionizing radiation. To date, the major concern for non ionizing radiation is its heating (thermal) effect on tissue. It is my understanding that the magnitude of the non ionizing radiation of wifi and cell phones is limited by regulations to be well below harmful in terms of heating of tissue. The leakage limits for microwave ovens is likewise regulated to be well below harmful in terms of heating of tissue.
Insofar as the potential harmful non-thermal effects of these sources are concerned, research continues. Clearly, as the number of these sources continue to increase, more data will be available to determine whether or not there are cumulative harmful non thermal effects of non ionizing radiation at the levels being produced.
In the meantime, in my opinion only, though it would seem prudent to limit ones exposure as much as practicable, it should not be because of being alarmed by non scientific information one may encounter on the internet. Rather it should be in recognition of the fact that the long term effects of non ionizing radiation continue to be studied.
Hope this helps.