well, the similar artists are not chosen by Last.fm. It's about how many listeneres the artists have in commom. Porbably people that listen do Shostakovich also listen to Stravisnky, and this is why they are 'similar'. It's fucked up, bu that's how it works;
How on earth are Messian, Schonberg, Sibelius. Brahms, Schnittke and Bartok similar to Shostakovich? !!!! Get a grip last.fm or preferably some ears and feeling! The only reason I am allowing Prokofiev and Stravinsky is because they were Russian. Again no mention of the orchestra or conductor. No surprise. When last.fm can be bothered to credit performers and composers I might buy something.