"Everyone is business today must be a trainer and mentor, not just the training department."

- Gregory P. Smith

Training is a value addition to the mankind. Imparting any skills to a human being is a contribution to the society. Moreover, there are hundreds of examples in the Corporate world where the permanent employees also  have ungratefully left the organization after getting trained on various skills, at high costs.
 
Providing training to temporary staff can be a blessing in disguise, because they can take up those positions in the organization, which fall vacant due to attrition (rampant these days ).

Consider the every day possibilities:

What if I stop watering my plants, coz the morning dew kills them? 
What if stop cleaning my house, coz it will get dirty anyway?
What if I stop savoring the present moment, coz soon it will be the past?
What if...
What if...
 
I could go on...but the fact exists that the quality of 'today' depends on the training given 'today' to the employee you have 'today'. 
 
 A phenomenon is a phenomenon, an entity is an entity, irrespective of its being temporary or permanent. More than merely ROI calculations, Training should be seen as an effective empowerment tool. Every one should be given opportunities to add value to himself /herself.
 
As the adage goes, if we give a fish to a hungry person, we give him merely a one time meal. But if we can train him for fishing, we provide him meals for all his life.
 
With such a high awareness and conviction that our HR colleagues have expressed on this subject, time is not far off when the process of "training" might get replaced by "coaching".
 
An additional two factors to consider:

1. The state of the company itself in terms of financial stability and pipeline density. If these are not healthy, a company may de-prioritize spending on temp staff, quite justifiably. These companies are forced to manage cash and business very tightly.

2. The Value-system of the Management short-term focused or long-term focused. There are many companies that has a Value-system to extract (exploit is a very strong word!) maximum out of people, in every transaction; concerned only on numbers like revenue per employee?? etc. These companies, albeit being in a position to afford training, may not do so.

Being an HR professional, I am convinced that Training is an investment and not an expense at all. It helps to look at training as a deliberate strategy, tuned with the Vision, than look at it as a bench-time activity or need-based activity.