Chili/Stew - Is it necessary to cook all the meat before adding to the rest of the ingredients?
What do you mean by "need"?


Will the stew have a deeper, richer, more savory flavor if you brown the meat first?  Absolutely yes, due the maillard compounds you alluded to.
Is it necessary to brown the meat before the long braise in the stew for food safety reasons?  Not at all.  You can cook it unbrowned, and it will be perfectly safe assuming you otherwise practice good food safety:  bring it up to cooking temperatures fairly rapidly, and cook it long enough.  Neither of these are usually a problem in stews.


In fact, some cuisines don't generally brown meats before boiling or poaching them, and still have outstanding outcomes--I am thinking of Tex/Mex taco fillings (not the ground beef kind, for example).

Now, as to should?  Personal preference.  I would choose to because I like the beefy flavors browning brings to the table.

Kenji Alt is now recommending just browning one side well, and then beginning the stew or braise, which I think is a very reasonable compromise.  See his Carne Adovada article for discussion on this.  This is the article that lead to his thoughts on browning ground beef that you cited.

. . . 

On re-reading your question, I wonder if you are implying that you are using ground meat.  Since you said stew, I was assuming the meat was not ground.  

If you are using ground meat, as in chili, which is essentially a ground beef and chili stew, you still have options.   

Browning will lead to more flavor, but require longer stewing to have a fully tender mouthfeel, as the browning will initially make the meat tough.

Just cooking through (greying, as it were) will lead to a firmer mouth feel than beginning the stew with raw ground meat, which leads to a soft, silky type of texture, almost.  This is actually traditional in some Cincinnati Chili recipes.