(1) The short answer to your question is that drinking wine makes a person satiated and strong while consuming olive oil removes a person's hunger but it does not strengthen him. In addition wine makes a person happy and therefore these two qualities:- strength and happiness, are the reason why wine is the only item of food apart from bread which has it's own specific individual blessing.

(2) I will explain this now in more detail based on the Gemara. Rashi, on the first Mishnah in the sixth chapter, at the top of Berachot 35a, writes that the reason why the Mishnah states that wine is the only fruit of the tree on which one does not recite Borei Pri Ha'etz, is because wine is an important drink and therfore Chazal gave it its own special beracha, in the same way that bread possesses its own special beracha of Hamotzi Lechem Min Ha'aretz, which is different than other blessings.

(3) The Gemara Berachot 35b (approximately two thirds of the way down the page) asks exactly your question:- what is the difference between wine and olive oil? Why did wine receive a special beracha and oil did not? After a few different attempts, the gemara finally answered that the difference between wine and oil is that wine is "Sayid" - it sustains a person - but oil is not Sayid. Rashi DH Sayid writes that Sayid represents a higher level of importance than merely "mazon" - food.

(4) The Ritva 35b DH Amri explains that Sayid means that wine sustains the heart and stenghtens it. [As a side comment, if I am not mistaken, there have been studies that balanced drinking of wine reduces the incidence of heart disease]. Ritva cites what Avraham Avinu said to his guests (Bereshit 18:5) "And Sa'adu (sustain) your hearts" from which we observe that sayid means to nourish the heart. In contrast the word "Zayin" (similar to Mazon) refers to removing hunger from the body, but it does not strengthen the heart.

(5) The Meiri 35b DH Kvar Bi'arnu writes in a similar vein that wine sustains the heart in the same way that bread does, and makes a person satisfied and strong.

(6) The Gemara continues and the conclusion is that wine has 2 advantages:- (a) Sayid - sustenance and (b) it makes a person happy, as it is written (Tehilim 104:15) "And wine makes a man's heart happy".

In contrast, oil does not possess this special importance and consequently remains like all other fruits on which one recites Borei Pri Ha'etz. In addition one does not always recite even Ha'etz on oil because if one drinks it on its own it is damaging and therefore one makes no beracha at all, and if one consumes it together with bread one also makes no beracha on the oil because the bread is the principal item and therefore one only says Hamotzi. The only time one says Ha'etz on olive oil is when one mixes it with another drink and takes it for medical reasons:- in such a case the oil is the principal part of the mixture and one recites Borei Pri Ha'etz.

Shabbat Shalom

D. Bloom