He is seen as a 'prisoner-of-conscience', a symbol of Putin's defiance to the West and to democracy. A kind of Aung San Suu Kyi of Russia. Every single politician in Russia (and in the West) uses this guy to score points for their respective ideologies. He is also a good symbol of the stupidity of Russian politics and the West's manifest failure to understand them.
Consider Medvedev. For some reason the West and Russian liberals decided that he is the liberal successor to Mr Putin, or even an alternative, and then duly expressed disappointment when that didn't happen. Keen to push his image of 'the liberal counterweight' to anyone who will still listen (of whom there is a surprising abundance), Medvedev recently moved to talk about reviewing Khodorkovsky's case. Putin uses Khorodkovsky as a scarecrow; Medvedev dangles him as a carrot to bleeding-heart liberals who see him as some strange beacon of hope who will come out of jail and reform Russia. Other presidential candidates also liked to talk about the guy during the presidential debates amongst themselves, with Prokhorov suggesting he'd let him out were he elected President. God knows what he hoped to achieve by that, but he polled surprisingly well. Probably because he was the only politician running who was actually interesting.
The basic party line seems to be this: with Russian courts corrupt and basically cowtowing to whatever the Kremlin wants them to do, the only option for this guy's release is for him to ask the President for a pardon, and for the President to pardon him. This sham, with Western politicians and liberals asking Medvedev to pardon the guy, has been going on for many, many years. This narrative is also batshit stupid because it runs against what the man in jail - Khodorkovsky himself, actually - wants. Neither him nor Lebedev have any intention to beg for pardon - because that would entail admitting guilt which they won't do - and Khodorkovsky himself has said in an interview to Novaya Gazeta that he would want to either die in jail or be released through the courts. Clearly if he doesn't ask for a pardon, the President will not have power for forgive him. Khodor remains in jail, Russia remains an evil dictatorship.
What is going on? The Russian equivalent of the Two-State Solution. Instead of focusing on stuff that really matters and ignoring even the main guy in the case so symptomatic of a massive problem - corruption in the Russian courts caused by overwhelming public apathy in politics and civic life - Russian and Western politicians simply sweep the issue under the rug and use the case out of context to push their own agenda which have little to do with reality. Meanwhile nothing gets done, the opposition continues to be unelectable, Western leaders continue to make bizarre claims about the Kremlin that don't reflect what's really going on, ordinary Russians continue to get screwed over and take it because apparently they don't know any better. Everybody's happy. You can tell how serious a Russian politician is in part by his stance on the Khodorkovsky case. So far nearly everyone is failing that test pretty miserably. Khodorkovsky's mother has recently called on Russians to come out onto the streets to push for change. Even she doubts it will happen. Judging by the comments, not very likely. Why try to reform a rotten society when you can simply... leave the country?