Not all investors who are accumulating bitcoin are rich; some of them are poor, but they are investing in bitcoin according to their discretionary income, which allows them to sort out their daily expenses and also hold their bitcoin investment for a long time. And with the help of the DCA strategy, they can easily accumulate bitcoin consistently, either on a weekly or monthly basis, when their money is readily available. It is only when you invest in bitcoin above your discretionary income that you are likely to get it wrong with your bitcoin investment because there will be a time when you will find it hard to sort out your daily expenses, and it might cause you to get off the game partially or permanently.
Rich and poor and people of all professions can invest in Bitcoin. One of the differences between rich people and poor people in investing in bitcoins is that rich people can invest more amount of bitcoins and poor people can invest less amount of bitcoins as they have less/small source of income.
I don't think so, if we are differentiating between the rich and average earning investor in investing then it can not be totally based on having more amount of Bitcoin than the average earner. Aside having the luxury to invest, we should also consider a thing about consistency which is a must factor for every serious investor that would love to accumulate Bitcoin to it's finest. The average investor can invest through the DCA approach and with time tend to accumulate better portion than the rich, the only difference i can detect is the comfortability of releasing funds towards his investment. If the rich investor does not have the quality intention and mindset to appropriately define his funds and grow his portfolio then an average earner who understands better can increase his portfolio over what the rich has installed already.
Being poor doesn't mean that you can't be able to solve your daily expenses or have discretionary income; it will only stop you from living a luxury lifestyle and traveling abroad for vacation. There are some investors who are accumulating bitcoin right now, and if they try to live a luxury lifestyle or accumulate bitcoin aggressively, they will find it very difficult to solve their daily expenses because they are not rich enough to do that, or they don't have a good discretionary income that will allow them to do that. If you can figure out how to invest in bitcoin in such a way that it cannot stop you from solving your daily expenses, even if you are poor, you can still accumulate bitcoin and hold it for a long time. Some people in the forum are poor, but yet they are still accumulating bitcoin because they understand how to accumulate bitcoin without finding it hard to solve their daily expenses and what they will achieve in the long run with their bitcoin investment.

You can do proper by adjusting your definition of poor, we have been using poor to define the average earner but appropriately being poor comes with the inability to provide one's daily survival needs, which means being poor results to living below the normal standard of comfortability. Not being comfortable imposes the incapability of securing any investment capital still going through the hand to mouth lifestyle. As long we are able to providing our needs then we can not be seen as poor, if poor then those who are unable to provide for themselves should be termed as what? An average earner can have his expenses sorted and still have left over funds that can now be diversified into his investment or being kept and saved for any functional purpose. @SuperBitMan also made further explanations.