The strength in using terms like Stalinist and Leninist over Communist and Socialist is that of practical government versus theoretical government.
In Marxist theory communism and socialism are abstract economic ideas about the distribution of goods and services and the ownership of the means of production. I might be getting this backwards, but socialism is the step a capitalism society takes after the clash between the owners of capital and the owners of labor. Marx did not invent some constitutional grounds for what socialism is other than that workers would own the means of production, namely land and capital, and become their own managers. As society adjusted itself to this government would be necessary for social cohesion, but would eventually dissolve into what he called communism. If socialism was undefined enough, communism barely has a word on itself. Basically society is in a perfect equilibrium without conflict between the owners and the laborers because they are the same thing.
So when someone calls a nation "socialist" no one even knows what it means. Are they socialist in the manner that Marx implied? Or like Sweden? Or Bolivia? It is simply a name, perhaps buzzword, thrown around to imply that they provide a lot of government welfare or have confiscated foreign property (or as my comp econ professor liked to say, "Socialism means that the US doesn't like you."). When we say "communist" we usually imply that a nation was under the sphere of CCCP, but I believe Marx would be appalled at the misuse of this definition (not to mention they entire skipping of the most important step towards communism, namely capitalism).
But when someone says that a state is "Stalinist" I can imagine a practical government. Stalinist governments are totalitarian, own all or most industries and services in a nation, attempt to maximize production through statistical and mathematical formulation, form communal everything (from farms to steel mills), usually are quite militaristic and are ruled by the iron fist of a single infallible (sometimes deity-like) leader. Basically post-Lenin Russia, Mao's China, and North Korea.
Leninist does not convey the same imagery. Leninist governments are much less totalitarian and are concerned with building wealth and properly distributing it. A good example is Tito's Yugoslavia, where workers, not the government, actually owned and managed the factories and businesses. Unfortunately Lenin was only around until 1923 (don't quote me on that), more than half of it involved in a bloody civil war with monarchists (paternal autocrats). We never had a chance to experience a real Leninist Russia, so we often affiliate Lenin with Stalin's Russia (especially because Stalin turned Lenin into a deity-like figurehead).
So I guess my point is, socialist and communist, eh not so good at conveying an idea of government. In America we sometimes call Canada socialist, or France. Marx would scoff at us!