True, the widescreen format means less vertical space and therefore more need to scroll for long documents, large images, etc., but widescreen (for better or worse) isn't going away. According to DisplaySearch, nearly 90% of portable computer LCDs and over 50% of standalone LCD monitors have a 16:9 aspect ratio. I honestly don't know of any laptop manufactures that still use 4:3 or 5:4, so you'd better hold on to the one you have. Those aspect ratios were close to the 3:2 used in very early 35mm cinema, and were used in TV and therefore computer CRTs. Cinema went decisively widescreen in the 1950s and now most TVs are widescreen LCDs.
Why the movement toward 16:9? Most likely because flatscreen televisions are 16:9 for "Full HD" (i.e., 1920×1080) video content, and it's cheaper to scale those panels down into computer LCDs. Also, with the same diagonal length 16:10 and 16:9 panels have less area than 4:3 and 5:4 ones (which are closer to being squares) and that also makes them cheaper to produce. At least the 16:10 aspect ratio that Apple uses for their displays is closer to the golden ratio (1.61803…) than the 16:9 screens.