I am assuming you found that information here
? If not please let me know so I can check for other places this may be listed and correct any typos.
We obtained the figure by estimating the number of key presses an average user makes in one year. Your math is correct but that is using our assumption that the average user makes 2.5 million key presses a year. Certainly not all users make this many key presses and with less key presses both the el cheapo keyboard and our Deck products would last longer than 4.8 months or 20 years.
Also to put things into perspective, for one million key presses to be made for one key on any keyboard you would need to hit the key once every 32 seconds for the entire year. Chances are most people do not accomplish that many presses, however certain niche sectors (gamers, coders, etc.) generally do.