Comparing the two 70-inch full-array LED LCD TVs on Sharp's Web site, the 732U has Sharp's Quattron quad-pixel technology while the 632U does not. In our experience with the 732U Quattron has little effect on picture quality in and of itself because the TV's picture settings allow viewers to prioritize color accuracy by essentially disabling the feature.
With Quattron disabled on the 732U we expect their picture quality to be very similar. Both have identical contrast ratios, LED lighting systems, and 120Hz refresh rates, according Sharp's Web site.
As far as we can tell there are not major differences between the two TVs. For more information, check out our full review of the Sharp LC-70LE732U.