That's not strictly true. You could license your commercial product as GPL, or (more likely) contact the library's authors and negotiate usage of the code under another license.
However, whatever your views on closed source products, they are still quite prevalent. IMO LGPL is a great license to get support from companies that sell these products, while ensuring that your software fundamentally remains free.
It remind me a few months ago the launch of meteor.js. I heard so much people saying that it was "not usable commercially"...
And the worse is that the same people have MongoDB in production with it's AGPL license.
If you are not intending to modify Mongo then AGPL is not restrictive, which may be OK. The database API is not usually considered as "linking" as it is a wire protocol.
So yeah, "contact the authors" can be hard, but an up-front agreement and price can make it pretty easy.