The P990 has been around for quite some time now, but just a few weeks ago the firmware upgrade that actually makes it reasonably stable was released. Or so I'm told, I'm happy about the fact that I don't have a P990. The P990 probably wasn't a very good idea from the start: too many new features in one single device is never a good idea, and as a consequence it started selling much later than originally planned, and was buggy in a way that makes Windows 95 look like a mature product (well, that might be an exaggeration...).
The P990 might be a bit worse than other smartphones, but it's not exceptional. To differentiate your phones from the competitors' products, you need new features. If you spend two extra months testing and fixing, one of the competitors will release a phone with the same new features, which means customers who want those specific features will buy that one instead.
Quality doesn't mean the same thing in commercial products as it does in non-commercial ones. I have a background in free software, and getting to terms with "quality" in the commercial sense is a bit hard. A defect is a problem if it has negative economic consequences, ie. if it's cheaper to fix it than to handle it with support, lies ("it's a feature!") or just ignoring the complaints.
The result of this interesting view on quality and the race for new features is that cutting edge phones are never stable. But smartphone customers don't want last year's products, so I guess we'll have to live with our buggy phones. At least you don't have to go to a service center to upgrade your firmware anymore...