Ganar vs Ganarse
When the verb "ganar" changes to reflexive, it actually changes the meaning, as with several other reflexive verbs. "Ganar" means "to win" or "to earn" and "ganarse" means "to deserve." Another way to say "to deserve" is "merecer."
Well, ganarse is not far off from deserve but it's not quite there. It's more like winning something, the act of getting something through winning it. Ex: "Me gané la loteria." You wouldn't really say "Merezco la lotería" it would mean something different. :)
So this brings up the question as to whether the reflexive case actually alters the definition of "ganar", as the original post claims. I would infer from your follow-up response that adding the reflexive does not appreciably alter the definition - perhaps at most it places an emphasis on the subject.
The closest cognate to "merecer" is "merit", which is essentially a synonym of "deserve", but has a subtle difference in connotation from "earn". Ex: one can earn a lot of money, but that does not necessarily mean one deserves or merits it. Similarly, one can deserve or merit a lot of money, but not necessarily earn it. Putting this together with your above comment, it seems that "earn" with the intimation of "winning" more so than "deserving" is a very good translation for "ganar" (or "ganarse").
Good point about shades of meaning. In your example, "me gane la loteria," is that using the verb ganarse or is it using the reflexive pronoun to emphasize something unusual or exciting, like "me compre un coche nuevo!" ? Would it be incorrect to say just "gane la loteria"? (sorry for lack of accent marks, my computer doesn't want to let me use them in the web browser)
Well, You have to know that in spanish we pronominalize a lot even when we are not really supposed to, like in "Me compré un coche nuevo" though you could probably take it as "I bought a new car for myself", we say it just meaning that we bought a car, But there are some other cases where it's just the habit ex: "Me comí un sandwich" the "Me" in "Me comí" is just a habit, not necessarily really meaning anything. It wouldn't be incorrect to say "Gané la loteria", in fact, it's just as correct as saying "Me gané la loteria", however "Me gané" would be a bit more normal, at least in northern south america (where I come from) simply because it's the way we speak. IN general: We pronominalize a lot even if there's no need to.