Whoever blasphemes against the Holy Spirit is guilty of an everlasting sin and will never be forgiven. So it is true. All sins are not the same. Catholic teaching distinguishes between venial and mortal sins, the mortal ones being the  more grave ones. Mortal sins are classified as such because of the harm that they do:  they kill charity that ought to exist amongst people. A mortal sin is  grave because it impedes an individual from being charitable towards others. While Jesus is obviously not referring to our classification of sins, he too understands that some sins are more grave than others. Jesus talks about a grave sin being that of blaspheming against the Holy Spirit. How does one blaspheme against the Holy Spirit? 
Jesus had just healed a demoniac and driven out of him an evil spirit. Present in the crowd as Jesus did this were some scribes. And as has become the case with other religious leaders, they refused to acknowledge the good that Jesus had done. And as is failing to see any good in what Jesus was doing was not enough, the scribes decided to up the ante in their disdain for Jesus: they attributed Jesus' healing powers to Beelzebul, the prince of demons. For reasons that were known to them alone, they refused to see the hand of God in what Jesus had done. It is this attribution that got Jesus worked up. It would have been tolerable if they simply refused to believe in Jesus (cf. John 10:38), but it was something else when they attributed the good work that God was accomplishing through Jesus to the evil spirit. By attributing the healing to the evil spirit, they were not simply belittling Jesus: they were also giving glory to the evil one. As scribes, they ought to have known better. 
Good cannot come out of evil. Good can only come from good. And we know that only God is good (cf. Mark 10:18). Healing of a demoniac is a good thing, and as such, attributing the healing to the evil spirit is the same as being spiteful of God. It is a sin that can never be forgiven. 
Are we spared of this charge? Not likely. How many times, because of jealousy, have we refused to acknowledge our brothers and sisters' accomplishment? There are times that we too have refused to see the hand of God working in our brothers and sisters. Sometimes we even go as far as belittling the good that God has worked in their lives. Behaving in such a manner equals attributing God’s good work to the evil one. When we do so, we too are guilty of sinning against the Holy Spirit.