There are a few things that IMO are likely to put new users off Git:
The Git culture is more command-line centric. While both tools do tend to focus too much on the command line (as I've said several times, command line instructions may be powerful and more fluent, but they are not a good marketing strategy) this is much more the case with Git. Whereas Mercurial has a de facto standard GUI tool in TortoiseHg, which is even the default download option for Windows users on the Mercurial homepage, Git has several competing GUI front ends (TortoiseGit, Git Extensions, gitk, etc) which aren't well advertised on the Git website, and which are all a complete eyesore anyway. (Black text on red labels? C'mon, TortoiseGit, you can do better than that!) There's also a much more pervasive attitude in the Git community that people who use GUI tools are not proper software developers.
Git has several out-of-the-box defaults that make perfect sense to advanced users, but are likely to be surprising if not intimidating to new users. For instance, it is much more aggressive about automating tasks such as merging (for example, git pull automatically merges and commits where possible). There is a case for fully automated merges, but most inexperienced users are terrified of merging, and need to be given the opportunity to gain confidence in their tools before unleashing their full power on their source code.
Documentation and inherent complexity:
$ hg help log | wc -l 64 $ git help log | wc -l 912