Google has decided that disadvantaged poor people, and others without mobile phones do not deserve to be treated equally. If you do not have a mobile phone you are obviously a second-class citizen and Google wants to take this opportunity to let you know that they don't care about you. And they do not care about the security of your Google accounts.
If your account gets stolen, Google will simply tell you, "See, you should have had a mobile phone, otherwise get lost you low life scum." Nice charitable attitude from one of the largest companies in the world. "You're poor? Oh we don't care if your account gets stolen and you can't recover it. Tough luck."
For evidence of this, see:
http://www.google.com/support/accounts/bin/answer.py?hl=en&answer=152124
Where there is no alternative method other than an SMS to your mobile phone, to recover your account. So if you don't have a mobile phone, you're screwed. Thank you very much.