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They are indeed different for semantic reasons. The <del> and <ins> elements are used to represent edits to the document [1] while is used to "label" names or misspelt text. [2] The <strike> element doesn't exist anymore but was used for styling text [3], much like CSS.

It's probably the same difference as vs. and vs. , so yes, sematic reasons

http://stackoverflow.com/questions/271743/whats-the-differen...

ins and del also define extended semantics attribute (@datetime and @cite), though I don't know that any browser does anything with them.

Browsers aren't the only tools for working with web content.

They're not new in HTML5, they existed in the HTML4 specification: http://www.w3.org/TR/html401/struct/text.html#h-9.4

And yes, the justification is purely for semantic markup reasons.