I said before how I remember Furor from FoH said that WoW was 1000x better than EQ before WoW came out. That was the idea at the time. Anyone who played EQ would be amazed by WoW. So, they were.. because WoW was coded much better and had hardly any zones and had instanced content. So, yeah, WoW did extremely well with all of those people who played EQ and then picked up more as the internet became more widespread among teens and adults who at the time would have thought it not 'cool'. Everyone is playing farmville on facebook now... back then nobody had an interwebs.
In the meantime, if they had introduced a cash shop at the time, it probably wouldn't have contained level boosts and just pets. It would have done the same. I think a lot of people initially liked the fact that you didn't have to pay anything to get anything and that it stayed to "You pay the subscription you get what anyone else could" (for the most part.) But a few mounts and pets a year isn't a big deal.
It would have been the same. I honestly don't see an issue with the buying of level boosting. I've RAF'd myself like 3-4 times in 6 years to level characters and get the rewards etc... I'd still rather RAF grind on a battlechest sale (5 bucks) pay for 2 months (30 bucks) get a month free on my main account (-15 bucks). And basically get 3x xp gain for 3 weeks for 20 dollars and get a mount/pet out of it. You would have to level the last 5 levels normally because they usually sell the previous xpac outside of the battlechest (panda land xpac won't be battlechest for a while after the new xpac comes out) but that goes fairly fast (especially after an xpac release where you can jump to new content and get higher xp for being carted through instances).
RAF if you have time can get you like 5-6 level 85s in a few days of grinding.
But, if they had included level boost up to 60 with a cash shop (they wouldn't) then no. Why would they ever do that? I don't think they would have added xp gains back then either. But as of now, for people who want to start playing the game, they have to level all through the old content if they're 'new'. It's not hard but then again the instance ques aren't the same as they are if you leveled during xpac and it's getting to be quite a ways away. BC difference 10 levels new xpac difference 40 levels.