I have never really thought or seen Bitcoin as beta software.
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According to the FAQ section from the Bitcoin.org website:
- Ongoing development - Bitcoin software is still in beta with many incomplete features in active development. New tools, features, and services are being developed to make Bitcoin more secure and accessible to the masses. Some of these are still not ready for everyone. Most Bitcoin businesses are new and still offer no insurance. In general, Bitcoin is still in the process of maturing.
So, even though the Bitcoin Core software is no longer in beta, Bitoin as a whole is still considered to be "in the process of maturing". I think that's a good explanation.