Just get a decent adaptor, I have an HP branded one which didn't require any drivers and has never failed to work in the literally thousands of times I've used in on loads of different laptops. Choosing a laptop based on it having a serial port is fairly dumb...
Also fairly necessary for some things, at work we use (well I don't, not actually my area, but you know what I mean) a piece of very specific diagnostic equipment, purpose built for the job at hand, it works via a serial port and the machine is setup in such a way that the diagnostic software cannot be copied to another machine, they won't even run without a 'security key' which is basically a USB dongle with some kind of encryption program on it that allows the software to run ...well anyway, this equipment does not seem to work via an adapter (we have tried it) ...I imagine there are other instances where this may be the case aswell.
Thus choosing a laptop because it has a serial port, is indeed something that for very specific tasks and under certain circumstances, is necessary now. As you probably realised, it isn't like there is a lot of choice in this regard now.
We actually use some older IBM's for this purpose, so I can't help you with a modern alternative I'm afraid.