Every brand has its problems. But with BMW the issue is they over-engineer things, so when you have a problem it's pretty spectacular/catastrophic. The S1000RR's are a lot more expensive to maintain and I should know, I have a few friends that campaign them even though they know their weaknesses. But hey, whatever floats your boat...
Like I said, I have never heard anyone refer to BMWs as unreliable, but there you go, you live & learn...