I thought the thread was about phones, rather than tablets, though that line is getting blurred. Nonetheless, if a tablet has a USB port rather than an SD slot, why not simply use an external SD reader? Personally, I find a USB port to be far more versatile than an SD slot on a tablet.
For smartphones, while a limited number of users might have a genuine need for an uSD slot, I doubt that the majority of users genuinely have a need for one. Skimming through this thead really quickly, I see those with a need mentioning a 50GB music collection, and a 1600 movie collection. Assuming that those two collections are legitimate and not pirated, I would estimate those two people make up less than 1% of smartphone users with non-pirated music collections that come near the 16GB. To support that assertion, this year, iTunes just announced it reached a record 25 billion songs that have been downloaded. But, in the middle of the year, I'm looking at a statistic that there were 575 million itunes accounts. A little division shows that the average iTunes user has downloaded 43 songs. That is, the average number of songs downloaded per user on iTunes is insignificant compared to the memory of most smartphones. Not that there aren't other legitimate venues for downloading songs, but at a glance, this indicates that users with multiple thousands of legitimately purchased songs in digital format are several standard deviations from the average and represent an insignificant percentage of smartphone users. I feel it's fair to exclude them from consideration in determining if uSD slot should continue to be supported on a smartphone.
The other legitimate reason - people shooting tons and tons of pictures on their smartphones - thousands of images that they'll never look at again; a vacation captured solely on a smartphone. I suppose that may be a legitimate need, if they want to save every image. But, it's not a huge stretch to realize that most of those thousands of images can be deleted, and the minority of good images can be uploaded to cloud storage (not that I'm a fan of cloud storage) to free up more room for more images.