In that article it was promised to the community that it would remain free. Quotes from it (emphasis mine):
Under an agreement announced on Wednesday 20th August , Red Gate will be responsible for the future development of .NET Reflector, the popular tool authored by Lutz Roeder. Red Gate will continue to offer the tool for free to the community.
James Moore, General manager of .NET Developer Tools at Red Gate:
I think we can provide a level of resources that will move the tool forward in a big way. The first thing we are doing is continuing to offer the software to the community for free downloading. The second thing is giving our product management and usability teams the task of going out into the community to get suggestions on how we can make this amazing tool even better.
We accept the fact that there will be scepticism, but we can point to a good track record of support for the community. People were wary a couple of years ago when we purchased the SQL Server Central community site, but over time we have won over many of our critics by investing heavily in the site and boosting its readership, while allowing it to maintain editorial independence. I’m hoping I will be able to sit here in a few years time and claim the same level of success with Reflector.
I understand that people will be sceptical of our motives and are concerned about the future of a great tool. I hope that we can win over those who are sceptical, through our actions not words, that we can be as good custodians of Reflector as we have been of SQLServerCentral.com.
Didn't something similar happen with SQL Prompt? This tool used to be a free offering before RedGate bought it... agreed, much work was put into it, but the price tag is high, making it more or less unaccessible for users working in a non-corporate environment. And I would be willing to bet that Reflector will become more and more expensive over time.