I’m not a formally trained expert, more like a hobbyist or maven, but a quick search of my Meta-Guide.com website seems to indicate that language models are generally statistical, whereas hierarchical language models are rule or tree based. So, a more precise distinction may be statistical language modeling versus hierarchical language modeling.
See my quick and dirty webpages:
· IRSTLM (IRST Language Modeling) Toolkit – Meta-Guide.com
· Language Modeling & Dialog Systems 2011 – Meta-Guide.com
· Rule-based Language Modeling – Meta-Guide.com
· SRILM (SRI Language Modeling Toolkit) 2011 – Meta-Guide.com