I find this whole argument about ease of use to be pretty uninteresting. Both types of bottom brackets are trivially easy to install and replace for anyone even sort of mechanically inclined who pays attention to routine maintenance. I have both, and they both work fine. I suppose it could happen, but a catastrophic bottom bracket failure must be a very rare event. In my experience they just become noisy and/or rough until I decide to replace them. Field replacement is so unusual that it's not something I would ever worry about.

The more interesting discussion to me is longevity. If I'm building an around-the-world ultra-low maintenance touring bike, I'm still going with square taper. As far as I can tell, there are two square taper bottom brackets on the market with 10 year warranties (IRD & SKF) while the longest external bottom bracket warranty I can find is 5 years from Chris King. Aside from my personal experiences and visual inspection of the seals on both types of bottom brackets, manufacturers warranty coverage would lead me to believe that a good square taper cartridge bottom bracket will last longer than a good HTII. Open to any evidence to the contrary, but I haven't seen any so far.