From a facilities point of view, investing in equipment is a complete minefield because the needs of the industry are forever changing and the equipment is also getting faster, more tools are continually being added to service the individual needs and ultimately improve 'workflow'. Investment today can be out of date in less than a year which therefore makes it difficult to keep up. The industry in fairness revolves around a trade show or two, such as NAB - Las Vegas or IBC - Amsterdam. A lot of manufacturers use these events to showcase new ideas, technologies and feature set improvement. They tend to be milestones, new products or when new advances are exhibited to sell their products, or ultimately to inspire present customers to reinvest with the latest and greatest! However even after a trade show it could be many months before this technology can be seen in a facility working - usually with a million and one bugs for 'early adopters' to contend with - its good to be an industry leader but you need nerves of steel sometimes.
I have sat with many clients who come to a meeting to discuss their individual project. They have a list, which during the session gradually gets ticked off (or not), as the particular tools or needs of their project are met. Many times I have enquired where these lists have been garnered and it usually is from a trade show! If it were that simple then everyone would be doing the job with the latest most expensive equipment. Most of the tools developed will now probably offer the minimum ticks on said clients list to get the job done.
I would personally suggest that equipment and the manufacturers used are only part of the equation and you ultimately use the expertise within the facility - at the end of the day that is what you are investing in. What differentiates them is the creative people operating the equipment, they are the ones that make it sing and dance, realising the vision of the project. I like to look at the grading theatre as the collusion between artists - the Director, the Director Of Photography and the Creative(s) pushing the equipment. They are what bring a project to fruition and polish the production for ultimate release.
The following is not a fully comprehensive list of manufacturers that are linked or working within the DI arena, these are just the more prominent within the field covering many of the different facets. I am not trying to champion one over the other. Hopefully the list should help make you aware of how many different companies are available - there may be some I have missed off by mistake, hopefully I have however covered the main players?