Purchasing and receiving the advertised services you've paid for in good faith, from a reputable company, should also be a fact of life.
That's the sticking point for me. They are part of a package and a selling point. When you sign up to the CC or whatever, the glossy brochure states "any Qantas lounge" but the reality is different. Quite a few people book long haul flights well in advance, and a consideration of carrier / schedule is lounge access, particularly longer transit stops (like Singapore). You book your tickets in good faith and then, a few months later, you're (not) informed that the lounge passes can't be used in Singapore. The fact that access to Singapore lounge was allowed when you booked seems irrelevant. I don't think that's fair whichever way you look at it. They can have caveats regarding periodic capacity issues etc, but these are blanket rules, for an extended period of time, with no prior notice. To me it's deceptive as they must know of these rules in advance given they are (supposedly) restricting access due to refurbishments/expansions. Projects like that don't happen without months of planning. Changing access rules doesn't happen without analysis, proposals and approvals.
Complimentary or not, they are a factor in deciding which airline and flight you book and pay for.