A lot of the industry folk, especially Vita owners, where a bit miffed that Vita had such a large absence at E3. In my opinion there is a clear reason for this.
1. Sony followed MS lead by delaying the announcement of their new console. Therefore, their focus was to push that last bit of PS3 sales. This meant that they had to be seen to promote the PS3 as a console that still had life in it.
2. Gamescom proved this as much. The Vita was prominent in Sony's Gamescom presser. Gamescom creates much less public awareness compared to E3, so this was a perfect place to show it.
So to conclude, Sony did not react to the bad press about the Vita no show at E3. They had to go all out and promote the PS3 then. Gamescom was always going to be the place where Vita shone.