Three reasons why LLL.com.au's are in demand:
1. Rarity (supply/demand)
There are only 17,576 (26*26*26) of these domains on the market. If PriceWaterCooper owns PWC.com.au and Apple owns MAC.com.au, there are thousands of other companies that have a budget to purchase the acronym of their brand/product.
The ability to quickly cash in on an asset considerably increase its value. There are only a few domains that have this attribute, namely numerics, LL.com.au, LLL.com.au and CVCV.com.au.
3. End User Value
Differently from numeric domains, LLL.com.au can be used as acronyms and easily allocated to specific end users.