All *we* care about (as current Linux users) is that. It will help boost Dell's sales of hardware to current Linux users, if they did take up that kind of policy.
Perhaps, though, the wider picture is that a pre-installed Linux would speed up adoption. Certainly, a pre-installed (and thus a configuration with hardware issues ironed out) Linux distro such as Ubuntu is perfectly capable for what, probably, a majority of people need. There are certainly very few users who actually *need* features which are difficult to use or install on Linux (gaming, complete compatibility with MS Office or a Windows specific program).
The audience Linux should be targetting is those who use their computers for the simple things - Web Browsing, E-mail and simple word processing/office suite work. By including Linux pre-installed on big manufacturers such as Dell, you will be hitting a large part of that audience. So what if someone buys it without understanding the difference between the OS's - it surely helps resolve ubuntu bug#1.