Please watch this. Sure someone running a channel named "valve news network" isn't completely objective in this case, he makes some very good points as to why this rumor is, again, just more hl3 rumor. Whoever started this rumor doesn't know how Valve operates in the slightest.
1. The employees at Valve works on whatever the hell they want to work on. They have wheels under their desks for a reason. They have no bosses except for themselves. This means that if enough people wants to work on hl3, they'll work on hl3. If this is a good bussiness strategy or not can be debated, but thats how Valve is run. Anyone claiming they "pulled people from a project for financial reasons" don't understand this.
2. Debunked by some Valve employers themselves in an email that was sent as a direct response to this case. The direct quote is: "Fear is the last thing that will ever drive a decision about what to work on"