There is no difference with web performance. When a company develops an online application and presents it to customers (it doesn't matter if they are outside/retail or inside/partner/employee), the perspective of the team that approved, created, tested, and released the application becomes, as a VP at a previous company explained to me, "interesting, but irrelevant".
Step away from the world of online application performance for a minute, and put yourself in the shoes of the customer; become a consumer. How do you feel when a site, application, or mobile app is slow to give you what you want? I'll give you some idea:
The stress levels of volunteers who took part in the study rose significantly when they were confronted with a poor online shopping experience, proving the existence of ‘Web Stress’. Brain wave analysis from the experiment revealed that participants had to concentrate up to 50% more when using badly performing websites, while EOG technology* and behavioural analysis of the subjects also revealed greater agitation and stress in these periods. ("Web Stress: A Wake Up Call for European Business", emphasis mine)
I know it comes from a competitor, but it is true. It applies to me; it applies to you. And web performance professionals need to step away from the screens for a minute and put themselves in the shoes of the people standing on the platform.
Everyday, your online applications change, grow, fail, falter, and evolve - the train is always moving. To the people on the platform, all they see is your train and how it's moving compared to the other trains they have watched go by. You worked hard on your train, polishing the brass, adding new cars, even upgrading the engine. To you, the train is a magnificent achievement that everyone should admire, especially now that the new engine makes it so much faster!
The customer on the platform is measuring how your updated train is moving compared to the MAGLEV bullet train on the super-conducting rail next to you and asking "How come this train is so slow?"
The complexity of a modern web site is astounding, and improving performance by 0.4 seconds is often a feat worthy of applause...among web performance professionals. From the perspective of your customers, that 0.4 second improvement is still not enough.
Web performance is a numbers game. As an industry, we have been focused on one set of numbers for too long. The customer experience, not the stopwatch, has to drive your company to the next level of performance maturity. To do that, you have to step off your online application train and take a cold hard look at what you deliver to your customers, alongside them down on the platform.