IT Employment

From over 12 years this is what I feel about in-house systems.

1. Incorporates the collective learning of the organisation
2. Slow to respond to industry and statutory changes thus the rate of obsolesence is high

On the other hand ERP as you have already mentioned in your question are INDUSTRY STANDARD that is they incorporate the learnings and best practices across the industry. This is possible because several customers drive the development of these systems by requesting features which in their individual opinions are important to their operations, thus building an application that incoporates several if not all of the best practices. Most ERP's have industry specific templates which when applied to the implementation automaticlly configures the product with the best practices for that industry - templates exist for automobile, technology, petrochemical, shipping etc

The obvious difference is of course the cost ERP systems do cost more then their home grown counterparts.