Content Keywords within Google Webmaster Tools does not display keyword phrases and keyword phrases are made up of more than 2 keywords. Some words are simply ignored in the Content Keywords, these include 'Web' which is not a stop word.
From Google's Mouth:
The Keywords list will sometimes exclude words that we determine to be
boiler plate text or common words.
Google as you know is pretty broad at times in what is what, but going back to the word 'Web' I assume 'Mini' is also a common word (But it's not a stop word) because Mini is used to describe a object/item Mini Lop, Mini Digger, Mini Car, etc etc. So I believe this is the case, and another thing said by Google:
Google explains that although it may not show up in the report, due to
possible Google issues, this should not impact the site in a negative
Page Issues with Mini Digger
I took a look at the page mini digger page and thought I'd give some constructive advice, you could increase the use of the word
mini digger once or twice more to give it more relevance. The other problem I stopped is the page could be incorrectly being processed by Google - This page and not investigating the others for example has 37 Errors, and 6 warnings on W3 Validator, while some are not so serious, sadly some are because the tags are not closed and this can cause all type of problems.
One small minor problem that should be easy to fix is that on your pages you are using
& while this isn't a serious problem as I'm sure Google has things in place for pages which contain invalid characters its best to fix the problem so you can move onto the next problems. Change all usage of
Additionally you may want to look into the headers of the page because they are not being processed correctly - for example at present if your trying to rank for the phrase
Mini Diggers Reading then this could be a problem because your headers are actually processing as
Mini Digger Hire inReading, London& Surrounding areas and Google may be ranking you for inreading without the space.. You can take a look here. Additionally you can check the errors I found at w3.
I hope you don't mind me taking a look and I know this wasn't your main question and you might even be aware of the problem but thought I'd add in my 2 cents, since your question relates to SEO it may be in your interest to fix the on page problems.