The Holo theme is required to be present on all devices that wish to carry the play store. If you write an app targeting 4.0 or higher that uses the default theme, it will look the same across all phones.
> However, you will lose the 2.3 users, who still hold a ton of market share.
Like with all massive ecosystems, change in the android world takes time. Google is addressing the problem and solutions, like instituting a required theme, are rolling out.
Give it a year, maybe a year and a half, and the need to support 2.3 will be much less pressing.
The Holo theme is required to be present on all devices that wish to carry the play store. If you write an app targeting 4.0 or higher that uses the default theme, it will look the same across all phones.