It just seems like "similar looking domains" and stuff has been a problem for ever and it still is. Will this still be a problem in near and far future?
If I'm used to visiting "capitalone.com" - and the site to activate a new card is something like "activatecapitalone.com" - that seems sketchy. It should be capitalone.com/activate or activate.capitalone.com -- I tend to simply avoid sketchy sites even if they appear to be from official sources.
Cell phones will let you insert a + directly in the beginning of the number (by long-pressing the 0 key), which will let the phone dial the correct number if you're roaming internationally.
In this case, the + is at the end of the number, which is not really a standardized thing. Landline phones won't have a + printed anywhere on them, for example. And you definitely don't want to long-press 0 to actually insert a + at the end of the number, because that's invalid.
First regarding the phone number Krebs at least speculates that since he didn't know what button to press for + maybe other callers pressed some button other than 0 (which maps to '+') which he claims all went to businesses callers would not want to have called intentionally.
Second regarding the website, towards the end of the article support for the rewards program claims that the website has not been published yet or is at least not finished.