Most of the manufactureers cannot get two lugs square with the barrel and 90%+ in contact with the reciever. Your solution could be done, but it would be a manufacturing nightmare.
Two lugs are more than enough strength wise, so there is nothing to be gained here.
If you want a safty lug just to make sure you are OK after the odd failure of the other two, i.e. triple redundancy or more, you can put in more non-bearing lugs or notch the bolt into the reciever. Paul Mauser did both on different models (M95 & M98).
Extra lugs do have the adantage of allowing a less than 90 degree bolt lift, and that is why some manufacturers use them. Three lugs allow a 60 deree bolt ift instead of the 90 degree kind. This is very nice, but it is not really for strength.