More to the point, they sound hard, so people won't be so quick to claim they've solved them.
On the other hand, case-insensitive string matching sounds easy, even if it's actually somewhat difficult due to the language dependencies mentioned above, so people will claim to have a general solution that fails the first time it's faced with i up-casing to İ instead of I, or the fact the German 'ß' up-cases to 'SS' as opposed to any single character. (Unicode does contain 'ẞ', a single-character capital 'ß', which occurs in the real world but is vanishingly rare. As far as modern German speakers are concerned, the capital form of 'ß' is 'SS'.)
http://en.wikipedia.org/wiki/Capital_%E1%BA%9E
http://opentype.info/blog/2013/11/18/capital-sharp-s-design-...
http://blogs.msdn.com/b/michkap/archive/2009/07/28/9850675.a...
http://www.personal.psu.edu/ejp10/blogs/gotunicode/2008/07/a...