I got the email this afternoon. Although mine said "Estimated arrival date: March 28, 2013". Perhaps yours was sent to spam? Or since people are apparently getting different/conflicting info in their emails, they likely had an issue with the emails and maybe stopped sending them before they got to you?
http://www.amazon.com/gp/product/B0050SXKU4/ref=oh_details_o01_s00_i00 If you scroll down to "Product Details" there is an estimated release date of "March 26, 2013" (as of my typing this, anyway).
None of the dates are the same, so Amazon obviously doesn't have a confirmed release, and nothing should be considered true until it comes from directly Rockstar anyway. However, this notice is the first update in information to pre-order customers that Amazon has made in the year since I pre-ordered it. While there may not be an official date yet, seeing anything from Amazon is a sign that things are gearing up.
edit: as I've seen other mentioned, part of the discrepancy in dates could actually be based on shipping methods/shipping times, with March 26th as the baseline. I did notice my pre-order was set for 2 day shipping, which would explain the arrival date being 2 days later. Still, the rest of my point remains. I don't count anything as FACT until Rockstar says, but I'm very excited about Amazon taking this step toward release.
Not sure who told you it's not available for launch day delivery, it says so right on the site in grreen text for me: http://www.amazon.com/Grand-Theft-Auto-V-Playstation-3/dp/B0050SXKU4/ref=sr_1_1?ie=UTF8&qid=1372824193&sr=8-1&keywords=grand+theft+auto+5
Do you have Amazon Prime?
If you have Amazon Prime you can get Release Date Delivery for free, and if you pre-ordered before it was listed on site you will still get it on release day.
if you are not prime I think you have to go back into you order and select the right shipping speed.
It's the same for Amazon US preorder.
Because that's what these companies do, they put placeholders up to get pre-orders.
WoW expansion: http://www.amazon.com/World-Warcraft-Mists-Pandaria-Pc/dp/B0050SZBP6/ref=sr_1_1?s=videogames&ie=UTF8&qid=1320155589&sr=1-1
etc.