So let's take Runes of Magic as an example, since it's what I used to play when I don't play SL. Runes of Magic is very much typical of the breed--free to play, free to download, free to wander through the world, cash shop for mini-transactions.
Can you buy mounts (horses, ferrets, snow berhu, tigers, whatever) through the cash shop? Yes. Are there other ways to get them? Also yes. Will riding from place to place improve time spent in the game? Definitely. Is it game-altering; for example, will owning a mount be the difference between one level and another? No.
Can you buy weaponry through the cash shop? Yes, but none of them are very good, and certainly few of them are game-changing.
Can you buy armor? Absolutely. Are there other ways to get armor? Yes, but it requires tons of gold for the good stuph. Can you buy gold? No. Can you buy diamonds and turn those diamonds into gold? That answer's interesting. It used to be: yes. So anyone with a trust fund and a yen to succeed could have the Best Armor EVAR and outclass those around them.
Then Korean and Chinese data-farmers got involved in the game. Over the year that they've been joining, and trying to woo people into trying their services, the Runes staff has gone from intolerant, to impolite, to lethal. At this point:
* use a gold-for-cash service external to the game, your account is banned. No appeal.So, for the most part, there's not a lot of buying-in taking place, now. There are people who have the best armor and the best weapons, and some of them are doing it illegally, and by and large there's so many accounts in Runes, the mods don't notice. These people are in the minority, though. Most people who have the really spiffy armor sets worked their asses off to get them.
* use a gold-for-cash service to buy things on the Auction house, your account is banned. No appeal.
* use a diamonds-for-gold exchange service to buy things on the Auction house, your account is banned. No appeal.
* Buy diamonds for use in the game with a credit card: you cannot use those to buy items in the Auction house. No exceptions.
* Get diamonds through answering consumer surveys: you cannot use those to buy items in the Auction house. No exceptions.
* Get diamonds through purchase of an authorized diamond card: you can use those to buy items in the Auction house, BUT you cannot sell diamonds on the Auction house.
* Offer up diamonds, gold or unlocked clean rune stones for sale in world chat, and if you are noticed, your account is banned. No appeal.
* Buy diamonds, gold, or unlocked clean rune stones offered for sale in world chat, while it's not automatic, if someone's paying attention, your account is banned. No appeal.
It does become--as so many MMOs do--a money game for higher levels, which is another reason I'm not as highly involved, these days. If you have the gold to throw at the Auction house for clean rune stones, and the gold to buy good equipment with the stats you want to combine with those rune stones, you can get some incredible armor out of it. And frankly, without that incredible armor, you're pretty much toast against some of the higher-level bosses.
Still, even with that, you can manage a good many fights just by going on all the quests, going on all the daily quests, and leveling up that way, enhancing the armor you're given along the way. It's slower, sure; but it can be done.