Even the smallest states have a few hundred legislators in 2 houses, and much shorter legislative calendars to get things done in.
Your question re:ballot initiatives interested me so I looked it up; signature-wise it takes 5% of DC voters distributed through 5/8 wards to get something on the ballot [0]. That's around 23,000 verified signatures. There are also the normal review periods/court challenges that are common in (nearly?) every state.
In Wyoming it's 15% of registered voters, nearly double DC, plus a fiscal review in addition to the normal court challenges.[1] I can't find anything saying direct initiatives are legal at all in Vermont, except constitutional amendments which come through the legislature [2].
In alaska (bigger but apropos since they legalized too) it takes about 30,000 signatures, and they have much stricter signature rules, including a house-district distribution rule. [3]
Overall it seems that DC is one of the easiest small 'states' to get something on the ballot in, although I have no way to compare how tough the court challenges are between states. Looking at the number of initiatives would be instructive but this comment is already getting long.
[0] https://www.dcboee.org/regulations/initiative_and_referendum...
[1] http://ballotpedia.org/Laws_governing_the_initiative_process...
[2] http://ballotpedia.org/List_of_Vermont_ballot_measures
[3] http://ballotpedia.org/Laws_governing_the_initiative_process...
Well, DC is a city, and Portland, Maine actually already voted to legalize marijuana in 2013[0].
If DC were a state, it'd be the first state on the east coast, but it's not. It's the first city that is not part of a state (and therefore not subject to constitutional rights allowed states), which is what makes this case very interesting.
DC is tricky because it's such a special case, but remember that it's much easier to pass an initiative at the city level than at the state level.
[0] http://www.mpp.org/states/maine/