I have read quite a few Ahādīth in which the Prophet (sws) has said:

Martyrs are those who die because of drowning, falling prey to plague, succumbing to an abdominal disease, or being buried alive under a falling building.

In another Hadīth, the Prophet(saw) is reported to have said:

Whoever is killed while protecting his property is a martyr.

I am a bit confused on this issue. All these forms of death are so different from each other, yet the common thing is the ending: the martyrdom. Does this mean that even if a person does not have much to his credit, he would still go to heaven if he died one of the above deaths?.

If all the texts of the Hadīth you have quoted first are collected and analyzed, it becomes evident that in most texts of this Hadīth a clause is missing which is making them quite ambiguous. The clause is Fī Sabīlillāh (In the way of Allah). In other words, these Ahādīth just say that a person who died in the cause of Islam and was not martyred in the battlefield for this very cause is a martyr also. This of course is quite comprehensible.

The following text of these Ahādīth is the basic one in this regard, and it can be seen from it that the words “In the way of Allah” are mentioned after each type of accidental death. In most other texts, this clause has been omitted by the narrators rendering them beyond comprehension. Abū Hurayrah reports:

I heard the Prophet asking: Whom do you count as a martyr. [Those around him] replied: a person who fights in the way of Allah until he is killed. At this the Prophet said: Then the there will be very few martyrs in my Ummah; [listen] a person who is killed [in the battle field] while fighting in the way of Allah is a martyr, a person who is infected with plague and dies in the way of Allah is a martyr, a person who drowns in the way of Allah is a martyr, a person who falls down from the animal [he is riding] and dies in the way of Allah is a martyr, a person who is inflicted with pneumonia and dies in the way of Allah is a martyr. (Musnad Ahmad Bin Hanbal, Vol 2, p. 441)

Besides the above mentioned ambiguity, it should also be kept in mind that in all such Ahādīth are omitted certain other details as well which must be taken into account; firstly, the person in question here is not the one who leads a life of sin; he is a pious and practicing Muslim. Other Ahādīth mention this qualification and which of course is based on the Qur’ān itself. Secondly, dying in the way of Allah should be his strong desire. This is based on the Qur’ānic precept that all of a person’s deeds are based on his intentions, and unless a person has an intention of doing some good deed an accidental happening in this regard will earn him no reward.

The Hadīth that says that a person who is killed while protecting his property is a martyr implies that a person who has laid down his life against oppression is a martyr. It is known that according to the Qur’ān (4:75), Jihād can only be launched against oppression and tyranny. A person who is killed in defending his wealth and property actually fights against the worst form of oppression and persecution, and therefore his death is certainly the death of a martyr. Again it is implied that the person in question is a practicing Muslim who is desirous of laying down his life for the cause of Islam.