I don't think the news from Nokia was as great as people had assumed it was going to be. Nothing came out and gave us an earth-shattering-must-have feature in the new Nokia phones exclusive only to Nokia. Couple to that the people who wanted to dabble in Windows Phone and were on the fence probably got a Lumia 900 and those people won't be upgrading as soon because they just got new devices and are likely (in the US anyways) to be locked into their contracts so they probably are not expecting massive sales for Nokia.
Couple that with all the finical issues Nokia has been having this announcement was not going to save the company unless they could have garnered an iPhone-level excitement. At least in the eyes of an investor.