Ti is generally SOFT, it has other good properties, like strength and corrosion free, but it's a soft material that can be cut easily like any other steel.
For a good lecture about materials check matweb.com
For example
Ti alloy compared to some
medium carbon steel
I have to repectfully disagree with your statements about Ti being soft and easy to cut. There are several issues that make Ti difficult to cut. I have designed several Ti parts and have supervised their machining and it is far from a routine process.
1. It does not conduct heat very well, so the cutting zone must be continuously cooled to keep the temps (can easily exceed 2000 degrees F) from ruining the cutter. Most LBS can't easily accomplish this.
2. Ti work hardens so as you cut the material gets tougher and tougher to cut, which also dulls the cutting tool.
3. Ti is springier (more elastic) than steel so it tends to deflect under the force of the cutting tool, which increases friction, and it turn temperature, which increases tool wear.
I don't blame the LBS a bit for refusing to chase Ti BB threads. If I had an expensive pair of chasing taps, I wouldn't want to take a chance on ruining them on a Ti frame.