I'm 90% certain those rumors are all wrong, not because I've heard any particular rumors to the contrary, but just based on Google's past behaviour.
How many Nexus devices has Google announced outside of a major press conference? Possibly one, if you want to count the Nexus S, though that was shown off prior to the official announcement at the 2010 Web 2.0 Summit. And how many press conferences has Google held without announcing them at least a few days beforehand? Zero. In fact they usually give at least a week's warning.
The Nexus S was the nadir of the Nexus line after the "failure" of the Nexus One to sell well through Google's store. Since then the Nexus line has gotten much more publicity and consequently sold much more, so I doubt they will return to the Nexus S style of doing things.
When the rumors of an Oct 15th announcement first started circulating they seemed entirely reasonable. However since Google did not send out an invitation to a press event last week I am fairly confident they will not make a stealth announcement of the Nexus 5 and Android 4.4 (KitKat) tomorrow. It is of course entirely reasonable that Google will announce an end of October event in the next week or so.
Of course I will be happily surprised if Google breaks with recent tradition and goes ahead and surprises us all with an announcement tomorrow. (Though not quite as happy as a lot of others. I'm excited about Android 4.4, but the Nexus 5 is reportedly far too large for my tiny little hands.)
Nexus One: - January 5, 2010: Android Press Conference - Invitations Dec 29th
Nexus S: - Dec 6th 2010: Blog announcement.
Galaxy Nexus: - October 11th, 2011: Ice Cream Sandwich Press Conference - Invitations Oct 13th
Nexus 4: - October 29th, 2012: Android Event (postponed due to Hurricane Sandy) - Invitations Oct 17th
Nexus 7: - Junes 27th, 2012: Google I/O 2012 - Registration Mar 27th
Nexus 10: - October 29th, 2012: Android Event (postponed due to Hurricane Sandy) - Invitations Oct 17th
Nexus 7 v2: - July 24th, 2013: "Breakfast with Sundar Pichai" - Invitations Jul 17th