Using one does thin the deck a little, but the fix for that would be to run as many lands as possible, yeah? This is the 2013 thread- we don't have the option of replacing them with basics. The only way to get more than the default number of basic lands is to inflate your deck to 63+ cards.
Wow, I typed all this up yesterday but it didn't post. I guess I got busy and never hit submit. Let's see if I can write it the same way I did yesterday:
In regards to deck building, in DotP 2013 specifically, I built my decks using the following process. This mainly revolved around the meta at the time when the game was the most up to date version available .
First thing I do is consider Goblin Gangland into the deck building. GG is the most powerful deck, and as such, it was the most common to run into. Some days, half my games were against GG. Every deck I built was built with that in mind. It needed to be able have a T5 win condition, and if there was a T4, that had to be in there as well. Barring that, the deck needed to be able to consistently win by T7. It would need cheap removal or cheap blockers, preferably with higher than normal Toughness, to disrupt GGs plans.
Now, the next logical step is, if I'm building my decks to optimize against the GG meta, then the other good players are too. Which means, beyond GG, the vast majority of decks I play against will have T4/T5 win conditions, consistently win by T7, and be able to remove or disrupt agro plans during T2-5.
As such, everything I built had the lowest possible curve while maintaining the ability to easily win by T7.
Obviously, there are exceptions to this rule. Control need not apply. Mana Mastery is also in another league, it plays by a different set of rules. However most of the decks in 2013 can be easily shoe-horned into a low curve agro deck. Take the example you brought up, Grinning Malice. This deck should top out at 4 5CMC cards with Demigod of Revenge. You do not need any other 5CMC card and you don't need anything in the decklist that costs more. All of your removal and all of the best creatures in the deck cost less.
If you take into consideration the fact that 2013 uses Hybrid mana you see why you don't need much mana fixing. Sure there are exceptions, IIRC the R/W deck has several cards that have funky casting costs, like WRR1 and that's a deck I would say needs 3 Fetchlands.
IF you build decks that way, you'll find that most of the builds you come up with fit within a deck that only uses 22-23 lands.