It is something I'm experiencing. Opera is so much diffrent from the rest of classical music that sometimes I think that if there wouldn't be connection coming from the fact that most of composers that wrote great operas were the same fellows who contributed to other genres, there would be clear partition between "classical music" and "opera" listeners. These are like two vast areas and it's rare to find person who is active listener of both.
I used to have great interest is piano stuff, now I feel that my knowledge about pianists got backward in comparison with opera performers because I know all major contemporary singers while when it comes to pianists I can hardly think of any whose style I could describe and give opinion. Of course I already estabilished my taste, I have my favourite recordings and know my share about great figures so there is no regression but I feel that my familiarity with the subject heavily lags behind since I undertook serious interest in opera.
Operas are long, listening to them is musically exhausting and these days I hardly can find some time to check out new symphonies, concertos or works of chamber music which used to be 99% of my listening time some time ago. To put it simple, the more I'm into opera the less I'm into all the rest of classical music.
While thinking about our community I get impression that I'm not the only one. Regular posters in opera section rarely or never discuss elsewhere (except community forum, but it doesn't count). Isn't Almaviva the guy who could ask "never heard of the man, did he write any operas?" when asked about Chopin, Brahms, Mahler or Liszt? Or about Richter, Mutter, Maisky, Rampal?