One thing the "no deletion" argument misses is that sometimes you have to delete data for policy reasons. At least two cases are important:

* Users ask you to delete their data. If you don't, and they find out you didn't, you have a problem.

* Legal action may require you to delete data. (E.g. you may find that someone uploaded child pornography to your system.)

This is actually a huge problem for companies like Google (where I work). When you have enormous volumes of highly reliable and durable (i.e. replicated) storage, it's actually really hard to make sure you can delete all copies of specific data reliably and quickly.